Yo dude, changing light cycle is no real issue if indoors as if environmental conditions are right then they shouldn't know what actual time of day it is anyway.
If i had to adjust like you say, i would do it in 6 increments of an extra 2 hrs darkness per night so then in 6 nights time they wake up at 4am and go back to usual 12/12 - that's only my personal preference as that sort of phase in they would never notice. If you're urgent and haven't got time and desperately need to do it, then just make sure you give them the extra 12 hours of darkness, not of light (i.e go to sleep at 4am then wake up at 4am) as that'd be the less stressful option of the two. And if they happy plants already then it shouldn't stress them too much tbh.