@Adrian_Williams I was working through the same conflict for a 70.3 race last weekend. I think you are on the right track by keeping the food type similar to what you have done previously and know works for you. Try the timing in a weekend prior and you can then be confident in the strategy. Looks like you have about 3 hours before as your plan right now; so take down this exact breakfast on Saturday when you wake up (normal time though - not 3:30 am 
) and then do your Saturday ride 3 hours later. If you have a few weekends between now and fondo you can iterate it down by 30 minutes to see if you can squeeze in some more 
on race weekend.