@Toaster79 I like you, so please don't take my opposing view as an opposition to you personally.
There are two different things we are talking about, root bound plants and plants starting to flower. I can't and wont speak on the root bound being the cause, because I always error on the side of bigger pots. I grow in 500 gallon beds, per plant.
"IF" we are talking about a plant that is flowering because the 15.5 hour light cycle on a clone plant isn't keeping the plant in veg..... Then in my experience you will loose a lot of time and energy on growing a plant that ends up lackluster. There is also no doubt that even though the days are getting longer, that doesn't mean the plant can't flower. Lets take the extreme of this..... Lets say there is 1 hour of light but tomorrow there will be 1 hour 2 minutes.......The plant would flower right? So there must be a cut off point where flowering will begin whether the hours of light or increasing or not right? Then we have to take into consideration the natural sunlight hours of the native geographic's of the plant. That will vary also right? A week or two of bad cloudy weather, that will effect things also right?
Let me put it another way. I have been growing outdoors for 15+ years. When I first started there was no internet sight I could go to and find out when the right time to put seeds out. Trial and error began. First I would notice last years seeds popping up around March naturally, must be time to pop seeds right? Well, time and time again a % of the plants would be very lackluster even though they were given the same nutes, start date, ext. Then I started to read and understand plant physiology, and begin to understand the factors that would cause my plants to flower early. Then over the next 5 or so years I started sprouting in May and the reveg plants were down to almost zero. Now I know, no matter what I do,(beside supplemental lighting) a % of plants will flower early, and I always have a back up to replace the flowering plant. This can happen in May, or in June and go back into veg before the normal August flower. I repeat, I will always replace a early flowering plant if possible.
Now I pop seeds in waves, March through April with the majority being on Holy week. I throw out the flowering plants and pop extra seeds. Done deal.
If you want to be 100% about seeds and especially clones not flowering early, then a simple 40w equivalent LED or compact florescent will keep a large plant in veg. When doing this, I turn on the supplemental lights at 4am. I try to stay away from wasted watts however.
