# MAINT-10 — the maintenance start hour is local time, default 19:00

Owner decision 2026-09-29 (option A). `maintenance_start_hour` was compared
with the UTC hour, so the shipped 10 started at 12:00 in a Belgian summer and
11:00 in winter. It is now read on the site's local clock, and the default moves
to 19 so the drain runs into the evening and night rather than the solar day.

Merges only after SAFETY-83 (peak guard outranks the drain at N=1): evening
drains meet higher house loads.

## 1. Which zone

Home Assistant's `time_zone` (`GET /core/api/config`, 3 s budget) at startup,
else the container's `TZ`, else UTC. One log line says which (WARNING only for
UTC). Resolved once per start: a zone change in HA takes effect on the next
add-on restart. The add-on image has tzdata (checked in `amd64-base:3.20`); the
CI image does not, so the tests grade DST on `tariff._EUTimezone` too.

## 2. DST

`maintenance.in_start_slot()` works from UTC instants only, so it does not
depend on how a tzinfo resolves a missing or doubled wall time:

- normally the slot is the local hour `start_hour`;
- clocks forward and the hour does not exist: the first hour after the jump;
- clocks back and the hour happens twice: the first pass only. Without this an
  aborted start (90 min cooldown) would start again in the 120 min repeated hour.

Every day has exactly one 60 min slot for every hour 0-23: checked against
zoneinfo for Europe/Brussels, America/New_York, America/Santiago (midnight
transitions), Asia/Kathmandu (+05:45) and Australia/Lord_Howe (30 min DST)
over all of 2026.

## 3. Existing installs

The Supervisor merges the shipped defaults under the STORED options, and saving
the settings stores every key (the reference install's blob has all 76). So
almost every existing install keeps its stored 10, which now means 10:00 local
instead of 12:00 (summer) or 11:00 (winter). Only a blob without the key gets 19.
The add-on does not rewrite a stored option: a silent migration would override
an operator's choice with no way to tell it apart from the old default. DOCS
and the release note (drafted on the PR, for the version bump) tell the owner
to set 19 if they want the evening start.
`tools/supervisor_shape_probe.py` §I measures this on Supervisor 2026.08.0.

## 4. What does not change

Only the start decision (`Maintenance.wants_start`) and the Home screen's shown
start time read the zone. `test_maint10.py` part 9 runs the real Controller
with start hour 11 UTC against 13 Europe/Brussels (the same instant) and with
12 UTC against 14 local (not the start hour): every command, claim, reason and
log line is identical. A `Maintenance` built without a zone reads UTC, as before.