In-park dining reservations open to everyone with a park pass reservation for a given date within 60 days as of sometime overnight.
Reservations for table service are not available for the preview dates.
Got Be Our Guest and Skipper Canteen on the 15th, Coral Reef Restaurant and Tutto Italia on 22nd, and Brown Derby on 23rd.
Wanted Oga's for 23rd, but all slots for parties of 2 or 3 have all reservation slots filled through July 27th.
Oga's appears to be limiting reservations for small parties to a very low number. Parties of 4 or more can still get pretty much whatever day they would like other than July 17th. I am guessing this is because they are limiting things to one party per table, and they don't want to waste those 8+ person side tables on parties of 3 or less.