Lithium started working for me after about 2 weeks, and at about 6 weeks my pdoc bumped it up to a more "therapeutic dose" of 900mg and that's what I've been on since. I think I've had minimal side effects from it and it has worked better for me than any other MS / AP I've been on.

As others have said you can REALLY tell a difference if you miss a dose even by just a couple of hours. The hypomania / mania creeps quickly but once you take the dose, it subsides.