See:
This is a great phenomenon for conifers. Actually it has been used commercially for years to get quick and continued growth in seedlings. In the basement now I have hemlock seedlings that have been growing continually for over a year with no signs of dormancy under just long days (16 hour photoperiod).
When I worked for the Forest Service I came across some references for pine where such forced growth can speed one through the juvenility process and get flowering years sooner than conventional planting outdoors. It’s a considerable investment though.
I can’t think of many situations where 24 hours or really long days can aid us with rose breeding except for quicker seedling growth. We typically do not have problems with stopped growth due to dormancy if the temperatures are warm enough and the light levels and photoperiod are reasonable. In fact it seems having at least some dark may be beneficial so stomates can get more practice opening and closing so they can be ready when they face the stresses of the natural world. I do have a rose descending back to R. virginiana and R. laxa that under a critical daylength sets strong terminal buds. It usually sets these terminal buds in early September. This rose is very very cane hardy and I think that is due in part to knowing when to harden off. When I take stem cuttings I can avoid terminals that set in a dormant bud or coax one out through just putting the plant under long days under grow lights. At least for this rose it appears daylength has more of an effect at setting terminal buds than cold nights.
Sincerely,
David
" Most rose cultivars, for instance, can be lighted 24 hours per day to increase production and quality without undue effects. "
Quote taken from link below:
Well I can certainly attest to the beneficial effects of continuous light on roses.
Two summers ago I took rose cuttings in the beginning of July. In the Fall…rather than leaving them outside, I brought them into my basement growing area and put them under lights for 14-16 hrs a day. That spring I planted them in the ground and boy did they ever take off. By the time they reached their official 1rst birthday they were huge…outperforming the potted grafted roses added that year and many of the more established roses that have been in the ground for a couple of years.
This year with my seedlings…I have been starting them off under lights that are on 24 hrs a day…continuing through to the first bloom of each seedling. They are then moved to lights on timers that turn on for 16 hrs. I have been able to get most seedlings to their first bloom (after disbudding the first bud) in about 6-7 weeks…with amazing overall growth to boot. As long as the electric bill doesn’t get too outrageous, I will likely continue this way until spring. I have seedlings now that are twice the size of the largest seedlings I took outside last year at the end of March!
I also have some ownroot roses that arrived this past Fall…ordered with the intention of growing them inside and taking them out in the Spring (wanted to try some ownroot versions of roses that have been less than cooperative in my breeding as grafted versions). I will certainly be lightyears ahead of where I could be with ownroots handled any other way…at least in my northern climate.
I use 24hrs too. Personally, Im too lazy to care about remembering the timing. Id most likely forget as scheduled details are beyond my memory. I use florescent lights which dont have the heat output or higher energy cost. Some of those gro-light bulbs can put out so much heat that Im amazed plants can grow under them without frying.
Jadae, I also use flourescent light bulbs. I switched all my light fixtures out this year to house the newer and smaller T-8 size bulbs (more energy efficient than the previous standard T-12 bulbs). While I did spring for the slightly more expensive bulbs that have a near 100 color rendering and a color temp range of 5000K…I haven’t really noticed a high physical temp in the immediate vicinity (probably have to get into the HPS fixtures before I would have that). I have about 22, T-8 fixtures set up right now…not all of them are in use just yet. But, I am quickly expanding to other shelves and turning more lights on every week…so I know I will end up needing to use all of them before spring arrives and germinations continue to emerge every day. Having 10-12 fixtures on doesn’t seem that big of a deal yet…but 20 might really start to rack up the $$ in the electric bill. As for the lights that are not on 24 hrs a day…I just use preset timers and plug the power strip into those. Otherwise I’d never remember to keep going down and turning them on and off either. LOL
BTW, when I replaced the fixtures this year…I had a ton of empty boxes stacked up at the curb on trash day. DH thought for sure that the police would pay us a visit to find out why we would need 22 flourescent light fixtures…he thought it looked suspiciously like I might be trying to grow something else in the basement! 
) ROTFLOL
Yes. I always fear the same thoughts from my neighbors. They already think Im odd enough with my plants lol. I’d probably do similar if I had a basement to use. There are not very many basements in this part of Oregon…they tend to submerge in the winter haha.
I have also noticed that rose seedlings grow faster under continuous light. The problem I run into is that germination almost completely stops on any remaining seeds in the flats. I am now using a happy medium of 16 hours on, 8 hours off. It seems to still work well for seedling growth and promotes better germination, possibly from the greater fluxes in temperature.