Ya, alot of women encounter communication problem with their mil. The best way is to ask hubby to convey the message to his mother. Its not wrong for u to ask "helper" to match your timing but its difficult because your "helper" happens to be your mil. So i hope your hubby will convey a nice msg to her nntelling her why to let lo stay up later so u can accompany for awhile. :) try not to be the person talking.
Mil has ways to look after LO. When we the dil said smth not in their favour, thy will say, 'u r lucky enough to hv me to look after ur LO' ): I wish i would hv my own mum to help to look after 😭
Your baby your rules, I think your mil should respect your wishes. Maybe ask your hubby to talk to her?