that number (most probly) is the number of seconds after January 1, 1970 00:00:00 hrs.
Thas is how php stores time .. using time / date functions.
Most probly .. phpbb uses this function only.
So if you want to change the date of start of forum to one month early than present date .. then decrease the corresponding date by 30*24*60*60 in your database.
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alibi
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