Hard to say. MGV is a large resort, so quite a few villas. While hot in July, schools are out so travel demand index is fairly high. While hotels can often get you in early morning, timeshares generally do not. I would say low likelihood of getting a room in the AM, but medium in early afternoon prior to normal 4pm checkin.
If I were you, I'd take an Uber to MGV (not too far), check-in when you arrive, have the front desk bellman hold your bags, then go enjoy the resort until you room is ready. They will call your cell phone to let you know once it is ready. Until then, enjoy the pool, bar, golf, tennis or other activities. A quiet few hours prior to the rest of your family joining, can often be nice and relaxing
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