Lvl 5 was easy for me, took half an hour, but I am not of the racing kind.
Lvl 7 took another half. Repulsors + mass of launchers + a pair of blasters do a great job here with the time limited part. Focus the advance on one side. Once finished below, dig up and open the chambers from above. Not hard.
Lvl10 is way harder (at least for me). 256hp drone leading a tsunami of creeper, stop that. Needed a MASS of blasters Soviet Army style.
Maybe using earlier those bombs and focusing on fire rate would make it easier. :P
Also, 5/5.