what do you mean last possable day?
You'll notice at the bottom of your pots there should be some holes. Peek inside and see if there are roots. If you see more roots than soil, that's when you transplant. They more roots they have when you transplant the hardier the plant will get (from my personal experience). this isn't something you need to do, just a suggestion. I do not have much room in my grow space so I conserve space by waiting until the budding half of their life to re-pot. In outdoor growing, I've noticed a huge amount of root growth in the budding stage. This is why I like to save the biggest size for later.
(last possible day meaning closest to the summer soltice ((longest day of the year)). after the solstice comes shorter days and budding period)
If you notice in my video my plants are a little too light in color. This is because i had to feed them EVERY DAY for there was not much soil, just roots, in the pots. I got lazy and did not feed them nutrients every day. To me, this was expensive and frustrating. this may also have been due to the lack of good nurtients. I used chemical nutrients I use for cloning, rather than organic nutrients and nutrients specific for budding period. This year I am strictly organic, kelp meal bone meal bat guano molasses and fish bone meal.