Longer than I can go on two bottles. How long that is depends on the time the race takes and the temperature.

If it's a little over what I would consider a two bottle ride I can extend it some by drinking well during the warmup and suffering a bit without water at the end. I used to do long runs with no water, getting a little bit dehydrated isn't that bad.

Most of the normal cat 4/5 M45 road races around here are no more than 50-60 miles. I haven't needed a feed for any of them.