A.G.
Honestly, your son eats more and sleeps more than any 5 month old I've ever heard of, so you may not want to mess with it! But look at this schedule - he's asleep more than he's awake until 4:30 in the afternoon -- no wonder he doesn't want to go to sleep til 10. You don't say what the problem is with just putting him to bed earlier, so I assume that he just doesn't go to sleep, in which case it sounds like you're going to have to mess with the naps. There is no power on earth that would make me want to shorten 4 1/2 hours of napping a day, but it depends on how much you want your evening back.
(And I'd recommend against finding a copy of Babywise. It sounds like you're doing the opposite of what they recommend, and therefore they will try to convince you you are ruining your child for life.)