So, Number Factor got 2 new modes today. 

Mini - Where you play on a 5x5 size grid.  This should offer an interesting challenge.  Drops start at 15.

and

Timed - As requested, I took Classic mode and put a 5 minute timer on it.  In this mode, every 20 drops adds a new row of gray discs.  You also, do not drop gray discs from above.  Only numbered discs.  Once time is up, the game ends.

Enjoy!