Ty for the feedback! :)
That level is the final level so I deliberately made it super hard. When you hit an enemy the time rate stays locked for a second. Also, the time rate regens slower at lower time rates. The trick for that level is to space out your hits by a second to maximum your low time rate, and channel calm at every opportunity. When the time rate is super low, if you just move a bit left or right then channel calm immediately you should have enough time to get another round of slow in.