i have about 16 plants that i am looking to get rid of to make room for 6 feminized plants. they are about 40 days into vegging and all i have is 6500k cfls and i was wondering if i could just put them on 12/12 with the 6500k cfls? or do i have to get 2700k? just til they show sex then i will be planting the females outside and disposing of the males. i prolly wont be focusing on them much but we will see what happens.. also how long does it take to show signs of sex?
Yes, you could do it, you just won't be getting the potential out of them. The key to flowering is the 12/12 cycle, not just the light. Sex will depend on the strain, some show soon, some later.
Most plants preflower and show sex between 4 to 6 weeks of vegetative growth especially if you go from a 24/0 light cycle to 18/6 they wiil start to show early at 40 days they should be showing you if not their close. Here is a picture of one of mine at 43 Days.