Has it been cold, wet or snowing lately where you live? I know that here is Colorado sometimes moisture will get into the brake and when it freezes over night will cause problem with the parking brake
Maybe moisture is freezing somewhere in the parking brake and not allowing it to disengage as fast as normal?
Maybe the cold is affecting the way the parking brake assembly is releasing?
When you park it tonight do not engage the parking brake and see if you still have the problem in the morning do not forget to leave the transmission in 1st gear and chock the wheel so it does not roll away