Yes it's possible to fly a hot air balloon at night.
However in some places it can be illegal for a hot air balloon to fly at night because of visibility issues.
If you're up in the air at night and a helicopter or plane flies through and doesn't see you in the air in your hot air balloon then it can cause a deadly crash.
So it's not advisable to fly a hot air balloon during the night.
Most hot air balloons are flow during the day.
I have seen a few hot air balloons up at night but only during a festival where they likely got permission and knew no airplanes or other aircraft would be in the area during the time the hot air balloon was flying.