Switching from 18 to 12...back to 18 hour light

Hey guys...need a little feedback if you could, please. Got a few seedplants going, wanted to sex them before I cloned them. I switched them from 18/6 to 12/12 about 1-2 weeks ago. I have now seperated the males from the females, but I want to switch back to 18 hour light to veg for awhile longer (and take my clones).
First of all....is this safe for the plants? Second, what can I expect when I switch back to 18/6....will they start vegging right away, again....or will there be a time period where they won't grow at all? I've heard differing opinions, so I'm hoping to get an educated answer here.
Thanks in advance for any help!!!
(if it makes any difference, I'm growing Euphoria Unlimited, and Tighty Whitey....and they are vegging under CFL.....will be switched to HPS for flowering....)

Anybody have any ideas about this? Would appreciate any feedback!
Thanks

well, from what I've seen and understand about switching back, it can be done, but can take upwards of 3-4? weeks, possibly up to 7ish i think, to revert them in ideal conditions. Reason being that when you put them under that 12hr light, they think fall/winter is coming, so they "flower". Switching them back takes time, because they have to stop the flowering process and that takes a lot of time apparently. I don't know the specific scientific reasons,but i do know it can be done, and i never noticed any harm to anything. It will add some time to your grow though, that I'm fairly certain of. Also, it will prolly put a little stress on your plants, but how much I'm not sure.

I've had a lot of buddies do exactly what you are. Hopefully you took clones of them into the 12/12, cuz it is my understanding that it doesnt always work out so smoothly. Recently though I smoked some Skunk #1 that was flowered, sexxed, then revegged, and it worked out pretty good.

next time you should only sex try only sexing one clone from each mother plant...then you will know the sex of your mother without having to flower her