Well I have calculated from the end of the maintenance of Patch 3.1 (Nov. 10, 08:00 GMT).
So putting in the 45 days and the total maintenence from then till now (25 hours), would it approximately be:

Dec. 26, 09:00 (AM) GMT.
Dec. 26, 01:00 (AM) PST.
Dec. 26, 04:00 (AM) EST.

I could be wrong, but this is my guess. ;-)