Fix time sync: delays in date/time too large for `chrony` to compensate

[mearlboro]

Motivation

context:
chrony synchronises hats clock with the router NTP server, incrementally
observer and router currently don't have real-time clock modules, the hats do
after not using the system for some time, large inconsistencies in time/date/year... between hats and observer

problem:
chrony can't sync date when it is behind by large increments of time
amounts of delay differ considerably between the two types of devices

possible solutions:

• setup a time server on the observer, from which the hats fetch the date - the issue with this is that the observer does not have an RTC so its date/time will easily be wrong. doesn't differ much from the router solution.
• install ntpdate, and run that at boot for all devices