Myfitnesspal just added an easy to use IF widget for pro customers.
https://support.myfitnesspal.com/hc/en-us/articles/10983207647117-Intermittent-Fasting-FAQ
Does a 12:12, 14:10 or 16:8 timer accessible from you food diary without all the coaching and other suggestions, etc. canceled my simple account, too much handholding on simple.
Answer
I recently purchased MFP for other reasons but it’s nice they’re trending in the right direction. These 3 out of the box settings are really limited and not relevant here (OMAD for me) right now but I’m hoping they let you customize at some point.