Taking time off construction.

I was upgrading and thought up an idea. "What if you could take 25%, 50%, or 75% off an upgrade's time. Don't understand? Let me explain. Let's say you are upgrading an Air Defense to level 5, and the amount of gems it took to sninjad it up was 200, if you took 25% of the time off, you would use 50 gems. If you took off 50%, it would cost 100 gems, and if you took off 75% it would take 150 gems. See what I mean? That would be way better than waiting the rest of the time or using 200 gems.