I took me 7 days to get from level 1 to 12, and by my calculations I was going to have to burn some diamonds at the end to finish the last level.
With the first crit update, made things more doable an I was going to be close.
But the last update made things ridiculously easy, I was able to get from level 15 to level 20 in just over 2 days, especially when I hit level 17 and each crit was giving me 3points, it was a breeze to finish it after that.

However, I did end up spending 200 diamonds on my way to level 12 because of where the very poorly placed button to buy energy pops up when you run out of energy. first time when it costed 100diamonds to refill and a couple times after when they reduced to 50.
Seriously who puts the button right on her pussy, where everyone is going to click, especially that at least for me was the place that was giving me more crits for the less amount of clicks.