[paulclinger]

I don't think it works the way author expects it to work, as the math is not correct. Think about `a+1 < 2` comparison. To remove +1, you need to change it to `a < 2-1`, not to `a < 2+1`; the operation needs to be transformed to the opposite one, which in this case would imply shifting the timezone in the opposite direction.

If you are asking about the timezone shift applied to a date, I think the engine converts the date to 00:00:00 timestamp and then does the timezone conversion.