The notes from Rev are absolutely right -- beyond that, I would also simply add, have you tried connecting more than once? As in, when it times out the first time, or even before it fully does and you know it will fail, going ahead and canceling it and connecting again? There's some sort of lag with the first connection attempt for a number of players at the moment, and that is something I am looking into, but the workaround is really simple.
Beyond that, if other games are working for you, I'd just make sure that it is the UDP rather than the TCP port that is forwarded. And, that the port is the same on both the client and the server, for that matter. If one of you changed the network port of the game to some other value, so that the two don't match, then that would explain the issue as well.
Hope that helps!