I am registered for a Manhattan GMAT prep course starting in February. How long after the last class would you recommend I wait until I take the GMAT? Is the following week after the class ends too early? Any advice?

We generally recommend 2-4 weeks after the class ends. You'll want some time to review, at the very least, and you may need some additional prep time if you weren't able to do as much work during the course for some reason or if you still have a ways to go in terms of your goal score.

So, for most people, yes, I'd say the week after the course ends is too early.

You have time to gauge this as you take the course, too - depending upon how flexible you can be in scheduling your test, you don't need to schedule it until 2-4 weeks before.