I have something for you...
Tell me what you think of it
About this topic and this fix, I think:
1. Board's time zone in the ACP has NO effect on board times.
It's just like Default Style, Default Language and Date Format, only a default preselection to help create new user's profile.
2. I confirm that the times stored in the phpBB DB are GMT/UTC ones. So they are COMPLETELY INDEPENDANT of their display by the create_date function.
3. For me this fix work well but can only be used in very precise cases :
o This fix is useless if your host forum server is not applying DST for itself (it means if the server is not in a DST concerned zone, or is not set to apply DST for any reason).
o The code of this fix must be adapt if your host forum server is in a 1/2h offset DST zone. By default, it adds 1h and do not check for the real value applied by the server.
o Next your users must be in the same state as the server to be sure that it's DST flag will switch at the right date, the same as their one (same geographical/political DST area once again).
In any other case, even if user's states use DST and are near the state where the server is located, the different states can switch at the same date/time or not, and this can change at any time by a political decision.
So this is not a good situation.
In fact, if you want to use the server information, your users must be in the same DST political zone !
If not, this fix can't do anything for you if you want to be always sure to have valid offsets at right dates.
In this case, the only solutions is to switch manualy, or to use user's local computeur DST settings because THEY are correctly set for their local DST political conditions.