Every time my my sister leaves her DS's (both under 2) with my parents, she also leaves a typed sheet with detailed instructions re when they should be changed, fed, what they should eat and when they should sleep. She even schedules in "playtime". I know for a fact that my mum smiles sweetly and then ignores the lot.
I think if she was MIL she would be deeply offended.
I think some suggestions like madamez says would be OK, but I wouldn't expect them to be followed to the letter.
My MIL had DS1 when I first went back to work (he was c. 8mths) and I invited her over for a few days beforehand so she could see how his day usually went, as we thought it might be easier for her if she knew what he expected IYSWIM, but it was always on the understanding that when he was with her, she was in charge and she would do things her way. I didn't always like it, but if you're not happy that her way will be OK, you shouldn't really be leaving DS with her IMO.
It is horrible when you first go back, and I understand your worries completely, but it does get easier.