Two things are important here
MZFW is based on bending moments, the more fuel in the wing the better so don't loose too much time.
You must stay within the CG envelope for landing. Fuel in center tank may have a serious effect on CG.
In case of doubt just put the plane on the ground then you will have all the time.
MEL ops procedures do not apply when airborne.
It's useful to carry a blank loadsheet in your flightcase.