That depends on when and where you ask them......if you ask them on a Sunday, or at night they'll get to it the next business day. If you ask them during business hours it takes roughly an hour or less depending on how many other students are needing help and if they're in the Student Help Desk. And it also depends on if you post it as a status update or post it in Support or not. They don't see status updates at all due to the large number of discussion threads being posted. Fastest way to get a response is to post it in the Student Help Desk.
So my answer is any where from an hour or less to the next business day depending on when the request was posted.