So I was thinking about, you could potentially code in scheduled patch dates or have a macro that triggered it when you logged in game(ie have a command /Schedulerepop for January 15, 2014 and update that date to DB). However you have to set the date out after the next mob repop. I have never looked at the code for this game but here is a rough idea.
PHP Code:
TimeOfSpawn = Random(7days whatever)
ForcedDayReset = CheckDBforRepopDate(whereveritsstored)
if(TimeOfSpawn > ForcedDayReset) Then
SetSpawnTime(ForcedDayReset)
Else
SetSpawnTime(TimeOfSpawn)
EndIf
And Do this whenever the intial /random is called when the mob dies. so make the /scheduledrepop command in game have a requirement of being 1-2 weeks out.