question about auto's light schedule

I have some lowryder 2's going right now and I have them on 18/6 and their dark period is from midnight until 6 am, that way its completely dark for them when they are sleeping, but I want change this so I can have their dark period be in the middle of the day instead. Is it okay abruptly change the light schedule like this with autos or would I have slowly change it over time like other plants? I want to change it because their grow space gets really cold at night without the lights keeping them warm (as low as 40 degrees). Another concern I have is that if were to change their dark period to the middle of the day it wouldnt be completly dark for them in their room because it has windows and I dont want cover them up because I have other plants in the room that need the sunlight and I dont want enclose the LR2s because then I would have to deal with ventilation and keeping the temps down. I know that autos can have 24/0 light but is this a disadvadvantage to 18/6 since mj supposodly grows during their dark cycle?

You can change any plants schedule by doin it durin their sleepy time!

Ya but will the sudden switch stress the plants or make them go hermie?

I just had to change my light cycle but this was due to heat, not cold,
It's summer here and It's been a really hot one.
It doesn't seem to have any negative effects.
But as someone said, do it in the dark period,
Extend the dark period until the time you want the 18 hour cycle to start.

And no, this one change should not stress them out @ all, actually!

sounds good, thanks for the help.

ANY PICS? wanna see that flowers without a sleep! lol...

They are only on day 25 and they just showed sex so there isnt much to see right now. The cold ass 40 degree nights have been slowing them down. I'll put up pics when the buds have started to form.