Hi,
The VS website ;
http://www.virgin-atlantic.com/en/gb...go.x=37&go.y=5
says that check in opens at 11am ( however it then refers to VS 8 & 24 which are LAX flights).
I would think ( not 100% sure) that at LAS check in would open about 4 hours prior to departure.
You may want to take a taxi to one of the hotel/casinos and leave the bags with bell services with a small tip and come back later and collect them before going back to the airport.
Regards
TBS