I think this game would be a lot better if your time remaining carried over to the next round/level. So if Level 1 has 20 seconds to finish it, and level 2 has 20 also, if you happen to finish level 1 in 10 seconds, you'd get an extra 10 seconds on the 2nd level.
That would make it way too easy I agree, though, it is frustrating to only have 20 seconds by the time you get to whichever round that is. I don't think I've been able to complete the board on that level yet