Co parenting

My kids dad has not been agreement about alot of things regarding summer visits. He lives 90 miles away. Our latest issue is that I am scheduled to pick them up Sunday since Saturday would end his 3 week time. And I said I would be there in the morning but he says he won't let them leave until 3. Now this disagreement is after he realizes that his next 3 weeks rolls into the school year cutting it short so he wants to interrupt my upcoming 2 weeks with my kids so he can have a whole 3 weeks before school starts. I said no, it's unfortunate how school starts so soon.

I have been done letting him take advantage of me, push me around, and manipulate me with his anger. If anyone has time please help me in knowing I am not wrong because if I dont want to waste my time showing up Sunday morning just to wait until 3. Can he actually keep them until 3pm if his 3 weeks is ended? And is Sunday considered my day?

Backstory-he did this to me once already. Although the last time during Christmas break he agreed to me picking them up at 12pm and later changed his mind to 4pm.