The Minhag of Las Vegas is that we do not know the proper night to observe Nittel, and that it could be any night of the year.
Therefore every night is treated as Nittel.
They do not hold of Nittel ending at midnight.
They also have a Safek (doubt) whether the time is when it is night where you are or when it is night in the middle east.
There remains a few hours each day in the spring and summer that can not be Nittel, but they are afraid that one might start learning and get too engrossed and not stop in time.
Hence, the casinos are kept open 7-24-365.
A few were found to violate the last Takanah, and actually calculate those few hours and pull out Gemaras then. To stop that they banned clocks in the casinos!!!
