I think at around that age, probably 2 full bottles per day is enough--8 oz. each. He's eating other foods so he's most likely getting his nutrients there as well. I would give him O. in the morning AFTER or with cereal, egg, whatever he eats for breakfast. You could also skip the morning bottle and give him a nice bottle before his afternoon nap. How long is his nap? You might want to try putting him down or waking him up a little earlier. Also, O. bottle with a little cereal or crackers, fruit, etc. before bed. If you are home, why not try feeding him his dinner a little earlier and down-sizing the "snack" after the nap to some water and two saltine crackers or 10 goldfish or the like? I remember it being unrealistic for my son to have 3 meals, his bottles, and two snacks per day--it was just too much food. I was like "where, exactly are the kids who allegedly eat like this??!!" Don't stress over the "set" feedings. He'll let you know when he's hungry. If he's eating lunch at noon, 6:00 is probably too long for him to wait for dinner but the snack should be minimal.
If he eats dinner earlier, he'll be more likely to have a better snack/bottle before bed and he'll sleep better. Good luck to you! (Hang in there, my dh is out of town also --for the next 9 days -- and it does STINK!)