Not that it would or should necessarily make a difference to his playing time, but I wonder what the reason is.
And, I get it. My daughter teaches piano and it's a constant battle to get kids to their lesson on time, and parents are always wanting to make last minute changes to the teaching day or hour after my daughter has scheduled the rest of her day and week around the scheduled lesson time.
Parents can be a challenge, and it's usually because they just have something they'd rather do or take their family that is more fun than practice or a lesson.