I'd even go as far as saying that every maintenance under normal circumstances always happens on Tuesdays, but that not every Tuesday is a maintenance day.
However, only if you're living PST, and not GMT+1 (or up), in which case it's actually always on a Wednesday, but not every Wednesday.
Although, you have to consider Summer/Winter time changes (+1 / -1 hour), which does not always happen on the same day (or at all) for every country nor area - in which case you could occasionally end up having maintenance on Tuesdays, where it normally would be Wednesdays or vice versa if you're UTC(+0) who would normally have maintenances starting on Tuesdays 23.00hr and extending to Wednesdays - but actually starting on Wednesdays rather than Tuesdays.
So you see, it's pretty clear - innit?