And in response to the OP... Let her adjust to the new environment for a week. When you do start nutes start real light. If it's never had nutes you don't want to shock the crap out of her again.
I can think of all kinds of naughty stuff I'd put plants though to see if it worked. While all the time running same strains in normal flower in my normal conditions to compare.
What would happen if you took your veg plants and decreased light time one hour per day or two until you got to 12/12? I was thinking it would trigger flowering more naturally then the hard flip. I know some folks who go to 11/13 then to 10/14 the last two weeks in flower to finish them more...
Interesting that the grapefruit you have is indica. Mine is 90/10 % sativa/indica. They stretch way out the first 2 weeks of flower. Don't remember what seed bank we ordered them from though.
Should be a max swing of 15 degrees between night and day temps. Don't let it get above 80 to 85 with lights on and i think 85 is way to high. So night should sit at 68 or so.
And... If the stems are thickening up you know that the roots are growing well. So give them a little more time and you will see massive growth at the top since you will have nice big plumbing (roots and stems) to uptake nutes and water.
You can turn the light up. Just move it up when you do then gradually lower it back down so you don't burn them. As far as the vert bulb there's a whole section on growing like that here. It looks like good fun though I've never done it! But if your not going to grow true vert flip that light on...
Anytime you transplant to a way bigger pot the growth on top stalls. The plant is concentrating on filling the big pot with roots. I've found it's about a week of stall then they will take off again. Patience and they will be fine.
When you change back they will take a week or so to revert back to veg depending on how long they were in flower so don't be alarmed if you don't see any growth for a bit. Good luck!
Don't change the lights twice. Pick 24/0 or 18/6. I do know for a fact that messing with it too much will mess them up. Either flower them or veg them. But don't mess with light cycles any more than you have to.
Personally I'm trying to decide about 24/0 and 18/6. Anyhow. Put them back on veg cycle. It's going to retard them a week at least but they will be fine.