You are not overeacting. If you want the child to stay i would change a few things. first tell mom that drop off is fast with a quick goodbye and off she goes. you will undress or help undress him. I would tell mom to text you or call when she is 5 minutes away and you will have him ready to go and have the door open ready to send him off. I would also tell mom that if she's not going to work with you on his "moods" then she will have to find someone else to take him.

If you have others to take the spot I think i would go that route. you've put enough time and effort into this and clearly mom isnt on board with you.