I don't think that's possible. In fact, Tables 2-7A and 2-7B in the manual say that the gate time setting is not stored in non-volatile memory. What you could do, however, is to store an instrument setting with the desired gate time using the save/recall function. Then you could bring that setting up with (I think) two keystrokes ([Recall] + [Enter]) after power-up if you save it in memory No. 1.