I made it to round 12, but then I just wanted to see the lose condition. I feel like as long as I keep throwing grenades (and due to my increased range, maybe even just as long as I keep attacking), the enemies couldn't do a thing. I enjoyed zooming around the rim of the clock when I had way too many speed upgrades.
I did encounter a slight bug where some grenades wouldn't explode. My guess is that the center of the grenade was too high to trigger the timer because the grenade was standing on its end.