I never booked any dining until after I had selected my FP because sometimes you have to be flexible to get the more popular ones. I didn’t make a lot of them anyway, but if I did, it was usually in the 30 days or less range. So for me, 60 is more than adequate. I do believe that if park reservations are gone and FP are back, it will probably be increased, but 90 days would be enough.
Add me to the list of people who remember making Epcot reservations day of at Earth Station or the kiosk in Germany, and remembers when it went to three days out, then seven, then I think it went to 30, but only for on property guests. However, since it usually wasn’t hard to do a walk up, I rarely made a reservation back then either.