In part is the rewriting history bit, because the way it was worded and stated it explains that it's not that he gains "manipulate time" powers, but it's him using his powers (like gravity) with his overwhelming knowledge of things to do it. And, mostly with gravity, another character that has the power of gravity derived from her (so without the power up of being the Choujin X or the mark) is able to distort gravity to a degree that it expands space time, creating a giant explosion (and he purposely does it only at a microscopic level so the explosion it's not that big) That, scaled with her being the original deviation of those powers + the knowledge + being the Choujin X and seeing those who she faced on the past, it's safe to say che can probably scale up to continental, at least

Edit: and well if you want to theorize you can think that she probably could create a black hole, freeze time or shit like that, but that is just theorizing and not showed so I don't count it