I would recommend when changing to flower try take time down gradually and stop at 13hrs fo a week, then after a week gradually drop to 12/12.
Im no pro but from doing that I have had great results with flowering time finish.
I only been growing for a year but that's what I found from doing, it's one of my tricks
But answering your question all plants have different time to finish and all depends on the environment.
If perfect for the plant you find things will nearly run same as breeder.
If you have messed up somewhere along the line it slows / speeds the plants finishing time.
But you can force finish by lowering the timer if you are in a rush,
I find time plays a big role in growing you just gotta find the sweet spot.... Just (imho) others will say different.
In my flowering room I use 11.30 on its not to save electric I just find that hours for flowering helps them finish around 8 or earlier so I chop. But my environment could have something to do with it I don't know but I tried flowering on 12.30hrs on,12.00hrson and 11 hrs on but the best so far is 11.30 on for my flowering room.
Good luck and hope I made sense lol