As the achievement says, it has to be Time Attack>Standard
There is a total of 8 fights, the first 7 are two rounds each at 50 seconds.
The 8th is Inferno, which is only 1 round but is the same as Arcade where he changes his style 3 times when you get a certain amount of damage done on him
Pretty easy to do with which ever character you find easy to spam a combo with, most people usual Raphael's YYY, I personally used Kilik with his XXY YY. Landing Kilik's combo twice and a couple of other hits usually won me the round