The thing is, even if it's NOT ready...a starter that at least is beginning to work, is STILL BETTER than pitching yeast without a starter. And POSSIBLY better than delaying pitching and leaving a wort sitting un yeasted, and vulnerable to other micro-organisms.
It may not be ideal, but if the yeast have woken up to start tackling your starter, than it going to be less of a shock for them if you dumped them into your wort.
There's is some thought that with starters the best time to pitch them is at "High Krausen" that means during active fermentation of the starter, NOT as we often do, after the yeast has flocculated. More than likely you are going to be close to high krausen at 12-14 hours, meaning the yeast will be pretty active, and if you pitch everything in like NNatic suggests you will be dumping yeasts that should be past the lag and starting to wake up.
I once had a brew schedule change and pitched a combination of a 10 hour starter and an extra tube of the same yeast which I picked up on the way to the brew, and fermentation took off really fast.