Be kind to your seedlings and match indoor light time with outdoor light time, therefore 16 hours.
No plant should ever be grown without a sleep period, it is extremely un-natural and highly stressful, especially for seedlings.
Every living thing needs an awake/sleep/awake/sleep cycle to function normally.
Cannabis when grown under lights is best performing when given at maximum an 18/6 schedule, it can only grow so much in any 24 hour period and 18 hours is maximum and optimum.
I would suggest the 16 hour schedule you are thinking about, this will provide ample growth for your seedlings and be the least stressful for them too.
Hope this helps,........
Organoman.