My latest theme submission was six days ago. Got a "we'll take a look" response the next day. And haven't heard anything since.
The one before that, I submit about three months ago. Got a "we'll take a look" response within a few days (hard to say when exactly) then got a "we'll accept it" response 19 days after that. This was in November, around Thanksgiving time. Also, the Theme Team was having their retreat during this time.
If you haven't got at least a "we'll take a look" message after two weeks, I might send a follow up message just to ask what's up. If you have, I'd just be patient. I get the sense that following up doesn't really speed up the process. They eventually take a look at everything, in my experience. It just sometimes takes a few weeks or so.