I think it's a 3 sided with bottom overflow box.
I was going to go with the 4 sided but my bulkhead is bonded to the elbow on the outside of the tank so i wouldnt be able to slip the bulkhead through the overflow then glass
Bulkheads are cheap, I would cut it off and add the extra piece to the OF box.
In any case, I think 48hrs would be plenty of time for the adhesive to cure but you can always check on the back of either, silicone or E6000 to make sure.
