Night skiing is available at no extra cost if you have a valid lift pass for 1 day or longer. Grand Hirafu's night skiing gives access to the largest areas in Japan till night skiing closing time, meaning you could potentially ski for 12 hours a day if you have the energy.
Depending on snow conditions, night skiing usually starts early December and runs through till late March. Please see the Grand Hirafu website here for planned lift operation date and times.