There are two checkpoints in Vegas airport when leaving, both of them with long lines of people, perhaps 200 persons each (this has been my experience year after year).
The first one is an immigration checkpoint, and the second is security.
The good news it that both of them run fairly fast (immigration faster than security). I think it's always taken me not more than 1 hour to clear both checkpoints.
So if your plane departs at 10am, leaving the hotel at 7am should be OK.
Please, someone correct me if I've got anything wrong here.
ETA: You'll need som time for baggage check in too, but it's no longer than 15 minutes in my experience.