Unlike some other companies I could name, SE seems to like using longer down-times in order to ensure everything goes according to plan the first time. Then, if they finish beforehand, they get to say "Hey look! We're done early! Isn't that awesome!?" The alternative is, of course, shorter downtimes followed by incredibly buggy additions that piss people off for a week, followed by a series of downtime/uptime/downtime periods while they try to fix each problem as they find it.