I'm a believer in transitioning any sort of change, lights, air, feeds, whatever. I just think it makes sense and gives the plants a chance to adjust with little or no shock. That's just my preference, not preaching it, just my opinion.
Interesting test I just did and unless in the end I see some issues, will continue to do this going forward. I went from 24/0 until about week 3 to get them well rooted, transplanted and moved to my veg cabinet @ 20/4 for about week, then 18/6 for 4 weeks, then out of necessity because I needed some time to work on my flower room, went to 16/8 for about 10 days, then 14/10 for a week, and finally 12/12 for the last 2 weeks.
2 strains, 2x PBK indica dominant, and 1x JTR sativa dominant. Both are at normal bud development for the time period, and the JTR saliva's are ahead of what I'd normally see after 2 weeks of 12/12 with a saliva dominant strain.
Sounds complicated but I'm in there 2-3 times a week for something or other and changing the timers for me is super easy, digital direct-wired timers control the outlets, not the devices, they turn the outlet on/off according to the schedule and take about 45 seconds now for the light timer, so no significant amount of work and they're rock solid/reliable.
If this holds and doesn't delay the flowering times (improvement with that saliva as far as I'm concerned) I'll be using it next round to see if it holds, as a bonus I save a couple of $ on energy consumption...