Move from veg to flower

Guys I think my girls are ready to go to flower my question is do I just flip the switch on them or do they need a rest period? They are currently under a 600 MH @ 18/6 and I want to go to 1k hps 12/12. Don't really know the age of the plants etc I picked them up half way through veg but they look great and keep growing everyday. Well thanks for the input will post pics if needed.

Csu

Me personally I just switch the photoperiod without the 36-72 dark period. I did that before and did not notice a difference. Based on my experience all I was doing was saving electricity for 36-72 hours.

Just flip 'em over to 12/12,no break.

Sweet thanks guys