My cat Pepper has been on a diet for about 9 months. He was definitely overweight and has lost about 2 pounds, but I'm starting to worry he's being underfed now. He just seems more stressed when he goes to check his food bowl and it's empty and will wait for the machine to dispense for hours before his feeding times.
He's a bombay, and I found some info online that says they should be under 15 pounds and some that says under 12. He's 12.6 now, and he still looks kinda chubby, but it's hard to tell because he has a big primordial pouch(loose skin in the belly area).
I know I should ask a vet, but I can't afford a vet visit.
Like others have said a healthy body fat for a cat is kind of determined by their ribs. You should be able to feel their ribs when petting them, but not be able to visually see them while they're lounging about or walking.
My cat is also a former fat cat that's been on a diet for years now. He has similar behavior to yours where he waits for his food for unreasonable(and sad) amounts of time, but is very healthy. It bums me out to watch, but he doesn't have the self control to graze freely.
He's got an automated feeder that goes off 3 times a day at specific times and then gets wet food for dinner. He's always stoicly waiting nearby for about an hour before any meal. That's way less than it used to be, but it still sucks that he spends 4 hours of his day just waiting and wishing to get fed. It actually really bothers me on an emotional and existential level, but I'd rather make the tough decisions and be sad than have him not be healthy and living his best cat life.