This is easy, I got 645 sec the first time.
Heres some tips, do what Unimarobj said and try to keep the big red ball that comes on screen for as long as you can and what I found was easier is to not get those extra cannon power ups because you can't control them and they sometimes knock the balls towards you and also it requires more attention to try and keep 2 things alive.
 "Bloons Tower Defense 3"){kind=icon}
 "Bowja the Ninja 2 (In Bigman's Compound)"){kind=icon}
 "Hover Bot Arena"){kind=icon}
 "Red"){kind=icon}