Hi and welcome to the disboards.
I would try the online reservation page several times a day. You're going from a 2 top table to a 4 so you could try for a party of 3 and for 4. People change their plans all the time so keep trying.
If nothing opens up you can check with the concierge at your resort after you arrive. Also, sometimes people have been lucky if they walk up to the restaurant when it first opens. However, you'll have to be prepared for the third person to be turned away so have a contingency plan if you don't have a reservation for 3.
Good luck.