Re-configure with config flow fails

[Hiekkaharju]

I'm trying to change the room temperature sensors of some quite old thermostats
When clicking "submit" on second form, I get "Unknown error occurred"
On first form I've tried both leaving coolers empty and writing null
Logs say (hope I got the relevant parts)

2026-06-06 10:27:10.324 INFO (MainThread) [custom_components.programmable_thermostat.config_flow] Second input data are valid. Proceed with final step.
2026-06-06 10:27:10.324 INFO (MainThread) [custom_components.programmable_thermostat.config_flow] Show final form
2026-06-06 10:27:10.324 ERROR (MainThread) [aiohttp.server] Error handling request from 192.168.0.123
Traceback (most recent call last):
File "/usr/local/lib/python3.14/site-packages/aiohttp/web_protocol.py", line 517, in _handle_request
resp = await request_handler(request)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.....

File "/config/custom_components/programmable_thermostat/config_flow.py", line 215, in async_step_second
return await self.async_step_final()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/config/custom_components/programmable_thermostat/config_flow.py", line 250, in async_step_final
return await self._show_config_form_final(user_input)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/config/custom_components/programmable_thermostat/config_flow.py", line 259, in _show_config_form_final
user_input[CONF_MIN_CYCLE_DURATION] = dict_to_string(user_input.get(CONF_MIN_CYCLE_DURATION))
~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/config/custom_components/programmable_thermostat/helpers.py", line 46, in dict_to_string
for key in time_delta.keys():
^^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute 'keys'

update: I created a new test thermostat. Reconfiguring it worked until I put something ( = 01:00 ) in the minimum cycle. That could be submitted, but after that on next reconfig the same error when submitting second form.

btw: manifest.json still says "version": "8.3", which shows wrong version in the header when wiewing the integration (hacs shows 9.0 as downloaded)