Time representation when exceeds 1 hour

No one is assigned
 t = os.date("%X", t-3600)
This is only valid for UTC+1. I'm at UTC+7 and to get valid result, i need to substract 25200 from t. Example:

> print(os.date("%X", 0))
07:00:00
As of lua wiki the format should be preceeded by an exclamation sign for the passed value to be treated as UTC:

> print(os.date("!%X", 0))
00:00:00
This should work for all time zones, no substraction required.