You're doing well for your first time growing... Be proud!!
Definitely go back to 12/12. 6 or 8 hours of light isn't enough photosynthesis time to allow for much continued growth.

Try to think about how it is in nature... In summer the daylight lasts 15 or 16 hours every day, and in winter the daylight falls back to about 12 hours a day or so.. If you strive to mimic this schedule indoors, your plants will do well and you'll see good results.