Ive been using 24/0 since the dawn of HID in the 70s. I used Halide for the first 20 years, until Hortilux started enhancing the HPS with some Blue. I went to 1000w Hortilux HPS in the 90s.
I also start seeds/seedlings under 1000w Hortilux HPS or 1150w Gavita DE HID, or a Gavita 1700e/LED. I blast them from day one. If we were in the mountains of the Andes, seedlings would be getting blasted from day one with huge amounts of light, and UVA/B. So I see no downside in blasting seedlings/rooted clones from the start. IMHO it makes them grow really fast, and develops strong side branching early on.
I grow big plants in large containers due to being in an unfriendly state to keep total numbers of plants down somewhat.
I start seeds/clones in 32oz Uline Deli Containers with Promix BX, and when theyre ready to transplant I veg them in 5 gallon grow bags for 45-70 days. When theyre ready to be transplanted the root system takes up all of the room in a 5 gallon container, usually, but is strain dependent. Fast growing Sativa dominant varieties usually fill out the space the fastest. Then when theyre ready to flower, and using an old Barneys Farm G13 x Haze that Ive had the mother plant for 12 years, I put the grow bags in 20 gallon containers and cut the bags off of the plants when ready to flower, and may veg them a week more in the 2o gallon containers, and when theyre done 70 days later, the root system takes up 100% of the space in 20 gallons of Promix BX. Ive not seen any short, or long term root growth problems vegging on a 24/0 schedule. I can lift the whole 20 gallons of soil out of the container using the stalk of the plant, and its completely root bound when theyre done.
I do have very very good ventilation/ Fresh air exchange, and temps really never exceed 85f. If you dont have good fresh air exchange the plants will not grow optimally. All in all if you have strong light, good air exchange, plenty of good soil, proper PH, and adequate amounts of food, and water, not much will hold them back. If even 1 aspect of the grow isnt optimal, progress will be slowed, or completely fucked.
Once every 7- 10 days I do turn the lights off for 4 hours to cool down the ballasts, but have also used 24/7 for 60 days veg, and never turned the lights off, and didnt have any negative impact on the plants.
I can get 22oz-24oz per 1 plant/G13 x Haze with 60 days veg. The G13 x Haze also sstretches 4-5 times its size when flipped, and I look for strains that stretch alot after flip. Im not takling about stretching where the buds are not thick either. Long, thick, dense colas. I also bend my plants over early on, and grow them like a forsythia bush. I also dont top.