On the weekends at prime time there is about 50-60 players online, weekdays about 40. If you cannot wait more than 15 minutes for a game then sins multilayer isn't for you. About sins online multilayer: Most competitive players like larger games like 4v4 and 5v5. It isn't uncommon for it to take more than 30 minutes to find a game, most experienced player go afk, alt tab or use windowed mode so they aren't idle in this period. Once you find enough players for a game wait time for the next game should be shorter because most of the players from the previous game will play again. As a new player expect some hardship, in game you will die fast and in the lobby you might get kicked from some games to make room for more well known players. You can start finding smaller games 2v2-3v3 around 11am eastern and 4v4 and 5v5 around 2:30pm eastern you may start having difficulty finding players around 11pm-1am eastern. (Note times are approximations and are general guidelines not exact times.) Normal settings for multilayer are everything faster, prates off, locked teams and quick start. Most games last 1-1 3/4 hours having 2 hours to play is deemed more than sufficient and most player will understand if you have to leave in a long game (just be sure to let the ai take over if you team can still win) for some reason its not using my lines I put in.

Any particular reason 5v5 is the norm? I'm surprised there are no large FFA games, it seems like the diplomatic intrigue in that would be absolutely engrossing. 

The problem is that the concern about getting stabbed in the back by an "ally" makes people want to dig in and play very defensively, resulting in very long games that often become stalemates.  You don't want to go attack the opponent next to you because your "ally" might backstab you.  Also, as a general rule, even every-man-for-himself no allies FFA games take a long time to play, too.  Game length is a big issue.

What's nice about the locked team games is that they don't take forever to play, normally just one-and-a-half hours.  The 5v5's are the most exciting games and sometimes offer players alternative ways to contribute to the team's victory.

Captain Siddy!  My [DT] bro.  Yeah!  Go get Diplomacy and getcher butt back in the game.