We are looking at making an early reservation for TuskerHouse 8am before the park opens. We are going to rent a wheelchair for my son, will the wheelchair/scooter rental booth be open before the park opens?
I believe the wheelchair/ECV/stroller rental locations in the park are open as soon as they allow anyone to enter the park - including for early ADRs.
I know you indicated preference to rent in the park, but another alternative is to rent off-site which will allow your son more use of the wheelchair - to/from parks, around your resort, DTD, etc. It will also be less expensive off-site if you plan to need the w/c for multiple days.
Offsite rental will also give you a choice of sizes, if your son is young, or just smaller than a adult a pediatric chair would be more comfortable, Disney doesn't offer anything other than adult chairs.
You may be much better off renting a wheelchair from off-site, especially if a standard wheelchair would be large for him.
If you click on where it says "disABILTIES" at the top of this page it will take you to the Index. One of the top items is the "disABILTIES FAQ" which will gives lots of useful information, including in Post #2 where people rent ECVs and wheelchairs.
Or, if you want an easier route to the FAQs, click on the link in my signature.
But if you definitely want to rent at a Park, the wheelchair rentals are open at the time the first Guests are allowed into the Park, taking into consideration both Morning EMH as well as any pre-opening breakfast reservations.