Ideally the coating should at the same rate, however that doesn't always happen. The slab isn't always the same temperature throughout, some areas may be a bit thicker than others, and there may be a draft in isolated spots. Those influences aren't a big deal and is a short while the slow spots catch up, all is tack free, and you're set for the LiquaTile coat.
Of course if the spots are real slow to tack free it could be a mixing issue, in which case it can take quite sometime for things to firm up, or if there are spots where the mix was real bad it they may never fully cure.
But odds are all will firm up soon enough.
If you do have spots that just don't hit tack free - do not apply the next coat. It's not a big deal to remove a few soft spots and re-prime, BUT it is a big deal to remove more than one layer of coating to fix things. The same applies for the top coat, if you have a spot that will not cure, do not apply the clear coat - deal with the soft spot first.
