You know, some exes are just looking for ANYTHING to complain about. If it was not the time, it would be the airport. If it was not the airport, it would be the drive to the airport. If it was not the drive it would be the airplane peanuts are too salty...I completely understand where you're coming from and thank you for sharing your situation. Every time Dad can book flights on the weekends, he does, because neither parent works weekends. So, it's not like she has to get up early for work. Her only beef is that it's past her other childs bedtime. Not to sound rude, but is that really Dad's problem?
You might just need to wait and see if she's complaining just to complain, or actually going to file something. Some exes like to threaten, but they won't follow through. What do you think?