My blue power is at day 12 and I moved her up to a 3 gal from the one..
My thinking is, my plant has another two months to flower and the roots don't stop growing when they go in to flower, they may slow down a little to put more energy in to producing flowers and seeds if pollinated..
I think you said you had three plants drinking twice a day? Maybe take one and move it up to a five, if you have room? And see how it does, bigger buds, or smaller buds then the others you left in the 2.5 gal ? But that is me, I like to experiment and see what happens..
Other question I have is what type of soil are they in? And how old are the plants?