For future reference, if the servers are down just after a restart, usually either the 8 pm or the 12 am one its likely due to an update like Cammm already mentioned. The timeframe for these is however long it takes to do really.
After an update, you can also expect the servers to be locked for a while and then unlocked and locked again. This is due to the way it handles people downloading the mission file, if it was left open and 130 people joined at once it would kill the server entirely, hence why it goes up, some people join, gets locked for a little bit to let them download, then unlocked for the next set, rinse and repeat until full.