Hi,

Yes, it is not possible to accurately compute the start datetime from the start date, start hour, and start minute fields without storing a timezone reference.

As you mentioned, Odoo server is forced to use UTC, which means that any date or time values stored without a timezone will be assumed to be in UTC. This can lead to incorrect calculations when converting to or from local timezones.

You can make use of the pytz library in Python. This library provides a timezone database that can be used to localize a datetime object to a specific timezone.

Eg:

import pytz
from datetime import datetime, time

# assume start_hour and start_minute are integers representing the start time
start_hour = 10
start_minute = 30
# define a timezone, in this case assuming the user's local timezone
local_tz = pytz.timezone('Europe/London')

# create a time object from the hour and minute values
start_time = time(hour=start_hour, minute=start_minute)

# get the current date in the user's timezone
today = datetime.now(local_tz).date()

# combine the date and time to create a datetime object
start_datetime = local_tz.localize(datetime.combine(today, start_time))

# convert the datetime object to UTC for storage in the database
start_datetime_utc = start_datetime.astimezone(pytz.utc)

By using pytz to localize the datetime to a specific timezone, we can compute the correct UTC value without needing to store an additional timezone reference in the database.

Thanks