S-ranking Chesnaught

I've been trying to S-rank Chesnaught for the past while using the standard Time+10 and Mega Start, but can't seem to do it. I am using MAerodactyl (9), Genesect (8), and Heracross (10). I seem to be wasting a lot of time looking for matches when the wooden blocks are still there, and the blocks seem to form just when I am about to make a match, wasting valuable time.

I have only once managed to finish the stage with 30-35 seconds left. The rest of the time, I am lucky to have 10-20 seconds left. Is there any good strategy for this, or is it all down to luck?