Hi there. I disagree, 3 hours may not seem that much but I find the east/west coast time change annoying, more so then when we travel to Europe. So be prepared to just go with the flow. 3 hours is just enough to make things silly and out of whack lol. We travel Toronto to Vancouver (EST-PT) a lot and it takes a few days to get used to it and then you have to turn around and come back lol. First time we did it with DS he was 1 yr old.
How far in advance will you be arriving before the wedding? What time is your flight, so your DS will nap on the plane right, or at least on an airport journey? I would see if you can get your DS to have as late a nap as possible before the wedding so as you say 5pm which is really 8 pm won't be so exhausting for him. Be prepared, you all will wake up early the first few days when you get there. Your body clock and bowels lol will wake you at 4-5am our time. So not sure where you are staying but when we stay with family, we quietly go to their living room and do some quiet activities and then head out for a coffee at Starbucks as to not wake the westcoasters lol. Sorry, not being doom and gloom, it's not that bad and you will adjust, it's more annoying. Coming back home I don't mind so much but you will be going to bed later and waking later so be prepared to have your DS sleeping in for a couple days.
I think it is best to just get him to sleep where you can get it. I don't really think you can do much to prepare and your DS has such a good base and sleep habits that it will be no probs getting into the swing of things once the body adjusts. have fun!!