No, most likely not.
The 4:00 time has been customary for partygoer admittance but is not set in stone as I understand it. Meaning Disney has typically granted that but could refuse at any point to admit partygoers until start time of 7:00 p.m.
Make your reservation after 4:00 to be assured of not being refused admittance and also charged the restaurant no-show fee per person.