Are you free feeding (he eats as much as he wants, whenever he wants) now? Do you have an idea of how much he's eating per day? You might want to consider measuring by amount, rather than by time. Our beasties now get a scant quarter cup (leaving a quarter inch or so empty in the measuring cup) of dry food in the morning, and they usually finish it within about 10 minutes! Ditto with the canned food at night, they are face down in the bowl until it's gone, and that doesn't take long. We do the occasional kitty treat, but it's more as a behavioral reinforcer/reward than as a staple in their diet.
If he has a lot of weight to lose, you might want to ask your vet for advice - you want him to lose at a safe rate. Crash diets aren't any better for kitties than they are for humans...