Apple says you "might" need to wait up to 90 days to associate a device with different iTunes account. "Up to" and "might"? ITunes store shows my iPad was associated with my account June 3rd.
iPad Pro 9.7-inch WiFi
That is correct, it will be up to 90 days i.e. if you only associated it an account today it will be 90 days before you can start another association, if you did it a week ago you will only have to wait another 83 days, if you did it 4 months ago you can remove the association etc.
Time to wait to associate device with new owner
