In my experience they will finish no matter what, even clones that barely root because they were taken late in flower. I have some that were just lower immature buds when the top buds were heading down the home stretch. They have fully matured despite their tiny root systems. Some are still in full flower mode weeks after the donor was chopped.
I also don’t think any of these plants were slow, they just got slow starts due to early struggles to escape their rapid rooter and were quickly shaded out. Also, my fastest plant, a sativa leaner (amnesia), was ready at about 75 days. The rest of my plants could have been chopped at day 85, but they were still stacking.
I still have clones of the Amnesia that was fast finishing up, I also left 6-7 branches that I left that were small less developed and shaded flowers still growing, I chopped the rest. I basically chopped her above the 3rd nose. This plant was sandwiched by the monster DSD I just pulled 1 lb.+ from and the monster WW that yielded 600g+, so life wasn’t good. But here are those flowers encroaching day 120, nearly 50 days after much of the rest of her could have been chopped, and nearly 30 days after she was mostly chopped
My longest plant, which had the least light in the tent for most of the grow, then had more light focused at the end was cut down a week ago, she probably could have kept stacking, but I have 100+ seedlings ready to go and she was in the way. Once she had light focused on her she finished up fast. But another interesting observation… A few of her clones that were taken mid flower (pictured below from a couple days ago), revegged and is now in mid to late flower, at day 115-120ish!
Basically, my belief is that light and early development plays a huge role in how quickly autos finish, as well as how big they yield. Stunt then early on and give them very little light, and I believe you could keep a clone of a clone running for 6+ months.
These plants want to keep living, however long it takes to finish. And I’m going to put this to the test with some good genetics that are known to finish in under 80 days…
If pollen shows up this week I’ll be pollinating some of those old clones to see what happens
Sorry to threadjack, but thought this might be helpful info for you and others