[Therlun]

There are two ways.
One is to simply browse the MP forum here and look for a game to join that starts or needs a replacement player.
(24-96 hours of time per turn to send in your turn orders).

The other is to hang out in the Dominions irc channel and hope for a blitz game (a game played complete over several hours).

I'm waiting for a blitz myself, but had no luck so far...