I get that at the same time (~22:30 GMT-8). It usually only lasts for 5-10 minutes (very rough estimate, never really timed it). Given the regularity of the time as well as the fact that it seems to happen every time I'm on the forums at that time (never kept track, but it's very consistent), I'd guess it's an automated maintenance thing. Maybe when it goes through and indexes, archives, etc.
