Starts at 11.00 and ends at dusk, best to think about just going for an hour or so for your first time unless with an experienced friend and on an experienced hunter.
Our meet is at 11am and they usually round up about 4/5pm - I normally stay until about 2.30 / 3pm as they will often go quite a bit further away at this point and then it becomes a long way to hack back!
the best time to turn away is when you come to a road, from there you can usually work out how to get back to the box, or a foot/car follower will usually be able to tell you. Otherwise, one of the field can tell you if there's no-one else going home at the same time.