Darkness: how much is 2 much?

Ok im growing 4 healthy plants outdoors. one of them is about 1 and 1/2 feet so i wanted to put it on a 12/12 light cycle to flower it.
My questions are:
A) whats the best thing to keep the plant in darkness at night and
B) if i cant get to the plants for some reason, how bad is it to have the plants in darkness for more than 12 hrs?

If your growing outdoors its out of your hands!! Just have to leave it up to mother nature

Tru. thats what i thought but...

"It’s possible to tell the sex of a marijuana plant early, and thus move male marijuana plants out of the main growing area sooner by covering a marijuana plant’s lower branch for 12 hours a day while it’s in a constant light vegetative state. Use a black paper bag or equivalent to allow for air flow while keeping out light. Be sure to set up a regular cycle for these covered branches. If light is allowed to reach them during the dark period, they may not indicate early at all."

.....why couldn't that exact concept be applied to an entire outdoor plant?

anything is possible.

if ur doing it outdoors then just wait untill the summer solstice is over, thats when the plants begins its flowering cycle, 1-2 weeks later ur gonna either see balls or pistles

OK well then figure out what you can use to cover the plant,maybe some kind of rigged box made with 1"x2" with a double blk sheet stapled to it for air flow??? and like you said what if you cant get to your plant after the 12hrs of darkness, if the light schedule is off it will stress the plant and if it does turn out to be female, you can wind up with a hermie from the stress, seems to me that your gonna have to schedule your life around covering/uncovering the plants, big responsibility if the plants arent right out the back door, and I thought not having a light timer was bad!!! dosent seem like the best of ideas IMO

yeah i would think your giving up a lot of control with a grow outdoors. I have heard of people sexing plants in first 4 days of flowering indoors though. all in all, mother nature will do its thing.