Hey mate, the questions will come down to personal preference but lets see if I cant help out.
When to flip is really better asked as when should I stop veg and begin flower. I dont mean anyone asking has it wrong, but the answer is easier when asked the second way.
Each plant will be a bit different in terms of stretch, but most growers will consider height as the first factor. Stretching can be up to 2x veg height in flower, so it becomes easy math.
Tent height (say 6 foot) minus lighting and accessories will give you available room to flower. Then divide by 2 and you will be around max height to stop veg give or take. Obviously this does not include super cropping technique if you chose to go down that road.
Beyond that is kinda preference in terms of sexual maturity, root mass, and grow length.
For lighting Id stick to 12/12. Anything under that is probably going to slow the girls up, its certainly ok to go 10, but your season will almost certainly take longer than if you went 12.
Some growers like to stagger from a max of 24/0, or more usually 18/6 down to 12/12. Like week 1 - 18/6, Week 2, 16/8, week 3 - 14/10, week 4 12/12, but you can just go straight to 12/12.
Again its genetics but the first cycle that triggers flower will signal to them to begin hormones to begin flowering. For some its the drop to 14/15, others need to be under 13 to start. The 12/12 will get them into starting no matter the strain.
I could be wrong and maybe theres some science to a dark period from veg to flipping, or maybe for certain it throws them into flower but its not essential.
I hope this has all been a clear explanation, and helps you make your decisions.
Im sure others will add things, and so far all the advice above this is spot on.