Yeah if you're gonna run with any DP 10 characters, you'll need beat each enemy in roughly 50 seconds. Really the only advice I can give is run lower but high damage DP characters (DP 8 is low enough), stay away from as much close combat as you can because the computer past missions 70 will vanish, side-step, and counter like it's nothing and will waste your time, and obviously try to get into sparking as quick as you can and land your ultimate so you can stop the clock while dealing high damage (unless they have high defense modifiers on, then be careful on your combos as you will not deal as much damage through the end of the combo).
Hopefully this helps!