I would not shoot if I could not clearly see my sights and clearly see the deer. Its not worth crippling the deer.
I would shoot if I could clearly see the deer and my pins, even if legal shooting time wasn't for another few minutes.

You have a sight light and can only see an outline of the deer? I wouldn't shoot if I wasn't positive I could pull off a fatal shot. Don't question your ability if you have complete confidence in your shot.

If you can't tell if its a buck or doe, its probably not enough light to shoot.