This information hasn't been disclosed, and they may never disclose it.

It could be attached to a regular daily timer or attached to an exact time (which presumably would be when the servers first came up on 3.1.) The only way to get an idea of when that is would be to get that information from someone who has a house that has not been accessed and can see the demolition timer in-game.

If you are at the point where you are keeping track of which houses look unused and which don't, more than likely you should just prepare yourself for a stake-out on the night demolition is supposed to occur.