Some shuttles run 24/7–on call in the wee hours rather than on a set schedule. Definitely inquire before booking.
Be aware that a lot of Las Vegas hotels charge a nonnegotiable “resort fee” which is essentially a way to advertise a nonexistent low rate.
I hate a resort fee. I once stayed at a ski resort in late summer. It was deserted and yet they saw fit to charge a resort fee that was about 30% of the cost. Never again.
Here’s the list of daily resort fees at most Las Vegas Hotels. Note that Marriott and LaQuinta amongst others do not charge a fee.