The server is always prone to random crashes throughout the day. Some hours it has a better tendency to be online because there are usually active members of the administration to restart it at different times; other times, the game experiences prolonged periods of downtime due to the most active Administrators being asleep - such was the case for the last several hours. Those staff members with the administrative privileges needed to restart the server can usually do so instantly if they're around when a random crash occurs, but if they aren't, the downtime is extended.
Furthering my point of them not being available around this time, it rarely undergoes maintenance at these "afterhours", and even if you're theorizing that such is the case, other sources can still confirm it; the twitter and
this thread typically being where the news comes first.
If the game is down, and no reason for acknowledgment of it being so on Twitter or here is made - the game has most likely crashed and is awaiting an Admin or Dev to restart it.
Also, since random crashes can occur at any time without prior warning, and since the personal schedules of Admins/Developers is subject to change, it's impossible to have any firm prediction on a timetable for the uptime/downtime.