I think it would be completely reasonable to request an amendment to the parenting plan if you can show that he has been late X number of times and it is impacting your ability to be at work on time.
I would ask to have it amended so that if he does not show up by a certain time, you leave. And make it a big margin, so that you can plan every day as if you were taking the girls to school. So, say he normally picks them up at 7:30. You need to leave by 7 if you are going to have time to make the rounds and get to work on time. Then you request that if he is not there by 6:55, you don't wait for him.
I was gonna say I think that's what I would do but honestly, I think I would request a change to the parenting plan so that he can't screw with you. Because I'm sure that's what he's doing.