Okay, so it doesn't matter how long the ice lasts if Danny's going to just blast right through it. He holds an arm up to protect his face from flying ice shards - anything that could get that far was going to be big enough to do some damage - waits for the blast to subside and the ice to fall-

The voidblob staggers and bellows-

And he snaps his fingers. The prepared fireball spell goes off, and the air in a five foot sphere around the voidblob explodes into flame. Hopefully, that and Danny's blast will be enough. Hopefully.