Actually, when Thor does the twirl the hammer to get esoteric thing, we usually have non-super speed characters witnessing it as a point of reference. So we can say pretty conclusively he's not unleashing such things faster than a normal human can think or whatever. So this does kind of come down to how easily he can actually generate fire. I'm not aware of him ever having done it, and I think it is safe to say it isn't a go to quick draw option in the same way a hammer toss or lightning bolt is. If he could make fire fast enough AND start raining down lightning bolts, he might have a shot.
But I think in all likelihood Dork is correct on the outcome. J'onn should be able to weather any initial attack long enough to at least phase underground, which then lets him unleash the TP basically unmolested and that's that.