I have used clen twice before, for 2 weeks each time.
One when I was at about 16% bodyfat and noticed very little improvement. And then again these past 2 weeks while I'm at 10% currently, and there was a HUGE improvement in the first week.
I would suggest you get much more cut before turning to clen. IMO clen should be used to assist the last bit of fat burning and to prevent catabolism when you're pretty lean already. I'll never use clen above 10% again, as it did nothing more than a clean diet will do.
As far as cardio goes - both times I've used it (currently at 120mcg/day) I have been doing 45 mins of relatively high intensity cardio every day - sometimes twice a day. And it didn't do me any harm
What's your diet like? That's probably why you're plateauing.