Hi, I have some automations that run during our off peak cheap rate, which is 00:30 to 05:30 local time. Meaning that it’s normally five hours, but on the change will be only four, from 00:30 GMT to 05:30 BST.
I have my HA timezone is set to “(GMT+00:00) London”
One automation tests for time range. Another triggered at a specific time.
Will the time seen by HA for these purposes change on the fly so to speak? I mean continue as GMT until 00:59 then one minute later show 02:00 BST?
It will change on the fly as you describe, which means automations that start on in the missing hour will not run.
The opposite will happen in half a year when you switch back to winter time, where automations might run twice that night.
Having got up specifically last year to watch the time change, for the first time in my life, I can assure you that Home Assistant does indeed go from 00:59 one minute, to 02:00 the next. This is based on ‘local time’.
This means that tomorrow is 23 hours long. The lost hour will magically reappear in October.
Anything that triggers specifically at times between 01:00 and 01:59 will not happen tomorrow, but will happen twice at the DST change in October.
Anything that runs for 5 hours over the DST time change will last only 4 hours, but 6 in October.
There is a very good reason why computer servers run entirely on UTC.
There was only one way to find out - watch the system at 01:59 GMT and see what happens…
With Octopus Energy giving Agile tariffs in UTC, HA shifting to BST at the stroke of 02:00 BST, and my inverter needing a manual change to the time settings, it all takes a lot of work to get timed charging of battery systems working correctly.
The good news is that my code worked perfectly, the inverter was auto-updated to the new local time, and the Agile timed charge worked over the DST change without a hitch.
