@DarkDragonMedeus It's already strongly implied that Mustache Girl got her powers off of the Time Pieces since, prior to her usage of them she's seen disposing of Mafia Goons with by her lonesome and with no powers. It also comes from the fact that she uses the Time Pieces in battle which are likely connected to her powers.
There's a chance AKM Sama is correct, but here's the thing. If you want to talk about speculatory, then there appears to be no evidence implying that Mustache Girl used the Time Pieces to rewind time on the entire planet. The Hat in Time wiki even says this but, again, there is no evidence proving that she actually used time manipulation to succeed this. Of course, time powers are the Time Pieces' main ability but that doesn't mean Mustache Girl used the concept of time to rewind the planet's age, Time Pieces can also create alternate pocket realities, bestow power and even portals and dream realms (actually this can qualify as an even higher tier because one rifts has numerous stars in the background and mustache girl even creates a pocket dimension with a time piece that has numerous stars and nebulae swirling in the background, so if the multi-continent level feat is considered wrong and these are considered legit than these can replace that feat).
That's speculation.
If you want actual clarification on the whole time rewinding factor, there is evidence to prove what is time manipulation, and what isn't time manipulation. There is a sound effect that plays indicating that time rewinds, and it's shown in two cutscenes.
This cutscene and
this cutscene. The first cutscene plays a rewind sound because time rewinds due to Mustache Girl dropping it (duh), and the second cutscene plays a rewind sound presumably rewinding time and the planet back to its previous state, it's something small yet it quite possibly applicable. However,
when Mustache Girl uses the Time Pieces on the planet, this sound doesn't play
at all. Infact, from what is heard, it sounds like actual destruction and rearrangement, at least from what it is going to be warped into. Mustache Girl's quote of 'let's mess with time a little' doesn't prove anything. It's a pun, a play on words because she's using a bunch of items with the word 'time' in them, it doesn't mean she's rewinding time or anything. A statement shouldn't be able to dictate and change an entire feat which is demonstrated on the planet itself. From what I know of the wiki's guidelines, we prefer actual feats/demonstrations with evidence over simple statements. There are some statements in the finale that can sort of prove the whole time rewind thing but again, they don't really seem definitive
Chances are, Sama could be right, but I still stand with the High 6-A feat because there is evidence proving that it is still legit and not a time rewind ability. It could probably count as a reality warping feat, therefore we can probably scale the characters to it with something like 'At least High 6-A' or something like that, this can also apply to the fact that it was warped in an unknown period of time, but it still seems almost instantaneous since the light engulfs the entire planet, thus changing it rapidly, almost nigh-instantly. If this is all false than i guess it can go back to 9-B or, possibly even get upgraded to a higher tier due to feats I've found that possibly involve tier 4.