I think you should refuse the early drop off on Monday - his colleague needing a lift is nothing to do with you, and it does not constitute an emergency.
(Ditto Friday, but you've got a plan for that one).
He has to realise he can't arbitrarily commit YOUR time to allow him to do whatever he feels like.
As i said before, Wife Mode has been discontinued.
HE chose this, so it's tough shit if it's not working out the way he'd like it to.
I think another text is called for, along the lines of: 'I'm reminding you again that the collection/drop off times to which we both agreed need to be adhered to. It gives the kids much-needed structure at what is a turbulent time in their lives, and allows each of us to schedule appointments etc. Dropping the kids early on Monday does not work for me, so you will need to change your arrangement with your colleague.'
If he asks why, reply that all he needs to know is that it doesn't work for you.
💪