Monster Life Info Guide

actually, if you nurture every day then lvl 30 will be achieved before your monster expires, at least every monster i've owned for a whole month got to lvl 30 with some days left.

I'm pretty sure that's not enough.
My monsters that will expire on the 16th (9 days from now) are only level 17, and I have been nurturing them religiously, 3 times a day and only when they ask for it.
I think monsters also need a good amount of playing in order to get to level 30.