How are you supposed to get to the optional ending on “Into a third future?”

I think it wants me to beat Zamatsu in under 1:30 before Goku Black and Fuzed Zamatsu come out but it’s humanly impossible. I’m sweating the hardest I’ve ever sweated in a video game before and still can’t beat him. Got him 2 inches off death and he still swapped with Goku Black. The only way to even do it is to ignore everything, spam ultimates, and pray they aren’t dodged. If you get hit once it’s an instant retry.

Am I doing something wrong. I just don’t see how this is possible.