If I remember right, you auto kill the small bombs by popping the the wind weakness ones.

If you're running out of time, then it's a DPS thing. Which means Song of Tormet is probably not your best choice for second damage spell.

Remember that you can freeze the big bomb mama by having it be nearby the blue bombs when they die. I think you're going to have to do something like

Watercannon
Offguard
Boost
Final Sting

Pop the bomb-ombs with mama over them for the free damage, then Final Sting nuke it.