its just to push off DMS, which occurs when you use particular types of malt. It gives a creamed corn taste. Since ur going gluten free u should be fine with 60, but 90 won't hurt. Just use a little more propane and take a little longer.
If you do decide to go with 90 minutes and ur going with a full boil instead of partial, just make sure have enough water to account for the additional 1/2 hour of boil off. Otherwise ur post-boil OG will be higher.
Bottled: Nothing :(
Kegged: Nothing :(
On Deck: Cider