diff --git a/common.js b/common.js
index 0a40d84..6ab05be 100644
--- a/common.js
+++ b/common.js
@@ -42,6 +42,8 @@ const PER_SET_OPTIONS = {
 	reloadSecs: { type: "string", def: "", id: "reloadSecs" },
 	allowOverride: { type: "boolean", def: false, id: "allowOverride" },
 	prevOpts: { type: "boolean", def: false, id: "prevOpts" },
+	prevOffToggle: { type: "boolean", def: false, id: "prevOffToggle"},
+	prevOffset: { type: "string", def: "", id: "prevOffset"},
 	prevGenOpts: { type: "boolean", def: false, id: "prevGenOpts" },
 	prevAddons: { type: "boolean", def: false, id: "prevAddons" },
 	prevSupport: { type: "boolean", def: false, id: "prevSupport" },
@@ -316,20 +318,35 @@ function getMinPeriods(times) {
 	return minPeriods;
 }
 
-// Clean time periods
+// Convert minute periods to a string
 //
-function cleanTimePeriods(times) {
-	// Convert to minute periods
-	let minPeriods = getMinPeriods(times);
-	if (minPeriods.length == 0) {
-		return ""; // nothing to do
+function minPeriodsToString(minPeriods) {
+	// Convert back to string list of time periods
+	let cleanTimes = [];
+	for (let mp of minPeriods) {
+		let h1 = Math.floor(mp.start / 60);
+		let m1 = (mp.start % 60);
+		let h2 = Math.floor(mp.end / 60);
+		let m2 = (mp.end % 60);
+		let period =
+			((h1 < 10) ? "0" : "") + h1 +
+			((m1 < 10) ? "0" : "") + m1 +
+			"-" +
+			((h2 < 10) ? "0" : "") + h2 +
+			((m2 < 10) ? "0" : "") + m2;
+		cleanTimes.push(period);
 	}
+	return cleanTimes.join(",");
+}
 
+// Trim, merge and sort minute periods
+//
+function processMinPeriods(minPeriods) {
 	// Step 1: Fix any times > 2400
 	for (let mp of minPeriods) {
 		mp.start = Math.min(mp.start, 1440);
 		mp.end = Math.min(mp.end, 1440);
-	}		
+	}
 
 	// Step 2: Remove any periods without +ve duration
 	for (let i = 0; i < minPeriods.length; i++) {
@@ -353,22 +370,21 @@ function cleanTimePeriods(times) {
 		}
 	}
 
-	// Convert back to string list of time periods
-	let cleanTimes = [];
-	for (let mp of minPeriods) {
-		let h1 = Math.floor(mp.start / 60);
-		let m1 = (mp.start % 60);
-		let h2 = Math.floor(mp.end / 60);
-		let m2 = (mp.end % 60);
-		let period =
-				((h1 < 10) ? "0" : "") + h1 +
-				((m1 < 10) ? "0" : "") + m1 +
-				"-" +
-				((h2 < 10) ? "0" : "") + h2 +
-				((m2 < 10) ? "0" : "") + m2;
-		cleanTimes.push(period);
+	return minPeriods;
+}
+
+// Clean time periods
+//
+function cleanTimePeriods(times) {
+	// Convert to minute periods
+	let minPeriods = getMinPeriods(times);
+	if (minPeriods.length == 0) {
+		return ""; // nothing to do
 	}
-	return cleanTimes.join(",");
+
+	const cleanPeriods = processMinPeriods(minPeriods);
+
+	return minPeriodsToString(cleanPeriods);
 }
 
 // Calculate start of time period from current time and time limit period
diff --git a/options.html b/options.html
index f210259..e296560 100644
--- a/options.html
+++ b/options.html
@@ -209,6 +209,10 @@
 								<input id="prevOpts1" type="checkbox">
 								<label for="prevOpts1">Prevent access to options for this block set at times when these sites are blocked</label>
 							</p>
+							<p>
+								<input id="prevOffToggle1" type="checkbox">
+								<label for="prevOffToggle1">Prevent access to options for this block set <input id="prevOffset1" type="text" size="2" title="Leave blank for no offset"> minutes early</label>
+							</p>
 							<p>
 								<input id="prevGenOpts1" type="checkbox">
 								<label for="prevGenOpts1">Prevent access to General options at times when these sites are blocked</label>
diff --git a/options.js b/options.js
index 6da60e0..eb89ead 100644
--- a/options.js
+++ b/options.js
@@ -127,6 +127,7 @@ function saveOptions(event) {
 		let delaySecs = $(`#delaySecs${set}`).val();
 		let reloadSecs = $(`#reloadSecs${set}`).val();
 		let blockURL = $(`#blockURL${set}`).val();
+		let optBlockOffset = $(`#prevOffset${set}`).val();
 
 		// Check field values
 		if (!checkTimePeriodsFormat(times)) {
@@ -166,6 +167,12 @@ function saveOptions(event) {
 			$("#alertBadBlockURL").dialog("open");
 			return false;
 		}
+		if (!checkPosIntFormat(optBlockOffset)) {
+			$("#tabs").tabs("option", "active", (set - 1));
+			$(`#prevOffset${set}`).focus();
+			$("#alertBadSeconds").dialog("open");
+			return false;
+		}
 	}
 
 	// Check format for text fields in general options
@@ -386,44 +393,116 @@ function retrieveOptions() {
 			// Get options
 			let timedata = options[`timedata${set}`];
 			let times = options[`times${set}`];
-			let minPeriods = getMinPeriods(times);
+			let minPeriods = processMinPeriods(getMinPeriods(times));
 			let limitMins = options[`limitMins${set}`];
 			let limitPeriod = options[`limitPeriod${set}`];
 			let limitOffset = options[`limitOffset${set}`];
 			let periodStart = getTimePeriodStart(now, limitPeriod, limitOffset);
 			let conjMode = options[`conjMode${set}`];
 			let days = options[`days${set}`];
+			let blockOffToggle = options[`prevOffToggle${set}`];
+			let blockOffset = options[`prevOffset${set}`];
 
 			// Check day
-			let onSelectedDay = days[timedate.getDay()];
-
-			// Check time periods
-			let withinTimePeriods = false;
-			if (onSelectedDay && times) {
-				// Check each time period in turn
+			let currentDay = timedate.getDay();
+			let onSelectedDay = days[currentDay];
+
+			// Check inputs
+			let useBlockTimes = times;
+			let useTimeLimit = limitMins && limitPeriod && ((limitMins * 60) < limitPeriod);
+
+			// Check option lock scheme
+			let lockScheme = blockOffToggle && blockOffset;
+
+			// Change 'if(lockScheme)' to 'switch(lockScheme)' if more schemes are added
+			let optionsLocked = false;
+			if (lockScheme) {
+				/** 24 hours in minutes */
+				const fullDay = 24 * 60;
+
+				// Setup
+				let earlyStart = Math.max(0, Math.min(fullDay, parseInt(blockOffset))) || 0;
+				let tomorrowSelected = days[(currentDay + 1) % 7];
+				let checkTomorrow = tomorrowSelected && ((mins - fullDay + earlyStart) >= 0);
+
+				/** If any minPeriod is active or within range */
+				let nearTimePeriods = false;
+				// Check time period proximity
 				for (let mp of minPeriods) {
-					if (mins >= mp.start && mins < mp.end) {
-						withinTimePeriods = true;
+					// Check time periods as normal if today is selected
+					if (onSelectedDay) {
+						if (mins >= (mp.start - earlyStart) && mins <= mp.end) {
+							nearTimePeriods = true;
+						}
+					}
+
+					// Check across day boundary if tomorrow is selected
+					if (tomorrowSelected) {
+						/** 'mins' relative to midnight tomorrow */
+						let shiftedMins = mins - fullDay;
+						// Check tomorrow's time periods
+						if (shiftedMins >= (mp.start - earlyStart) && shiftedMins <= mp.end) {
+							nearTimePeriods = true;
+						}
 					}
 				}
-			}
 
-			// Check time limit
-			let afterTimeLimit = false;
-			if (onSelectedDay && limitMins && limitPeriod) {
-				// Check time period and time limit
-				if (timedata[2] == periodStart && timedata[3] >= (limitMins * 60)) {
-					afterTimeLimit = true;
+				/** If timelimits need to be checked at all */
+				let checkTimeLimit = onSelectedDay || checkTomorrow;
+
+				/** If a current/upcoming timelimit does not have enough time left */
+				let nearTimeLimit = false;
+				// Check time limit proximity
+				if (useTimeLimit && checkTimeLimit) {
+					/** The amount of the timelimit that can be used before options lock */
+					let lockTimeLimit = limitMins - earlyStart;
+
+					// Positive lock TL: Check only the active time limit period
+					if (lockTimeLimit > 0) {
+						let secondsLeft = lockTimeLimit * 60;
+						if (timedata[2] == periodStart) {
+							secondsLeft = Math.max(0, secondsLeft - timedata[3]);
+						}
+						nearTimeLimit = secondsLeft <= 0;
+					} else {
+						// Negative lock TL: Complex interactions with timedata/time periods/day borders
+						//   skipped for simplicity
+						nearTimeLimit = true;
+					}
 				}
+
+				optionsLocked = (!conjMode && (nearTimePeriods || nearTimeLimit)) ||
+					(conjMode && (nearTimePeriods && nearTimeLimit));
+			} else {
+				// Check time periods
+				let withinTimePeriods = false;
+				if (useBlockTimes && onSelectedDay) {
+					// Check each time period in turn
+					for (let mp of minPeriods) {
+						if (mins >= mp.start && mins < mp.end) {
+							withinTimePeriods = true;
+						}
+					}
+				}
+
+				// Check time limit
+				let afterTimeLimit = false;
+				if (useTimeLimit && onSelectedDay) {
+					// Check time period and time limit
+					if (timedata[2] == periodStart && timedata[3] >= (limitMins * 60)) {
+						afterTimeLimit = true;
+					}
+				}
+
+				optionsLocked = (!conjMode && (withinTimePeriods || afterTimeLimit))
+					|| (conjMode && (withinTimePeriods && afterTimeLimit));
 			}
 
 			// Check lockdown condition
 			let lockdown = (timedata[4] > now);
 
 			// Disable options if specified block conditions are fulfilled
-			if (lockdown
-					|| (!conjMode && (withinTimePeriods || afterTimeLimit))
-					|| (conjMode && (withinTimePeriods && afterTimeLimit))) {
+			if (lockdown || optionsLocked) {
 				if (options[`prevOpts${set}`]) {
 					gNumSetsMin = set;
 					// Disable options for this set