How long can a broody hen get off her eggs?

I know this question has been asked, but I searched the forum and can't find the answer.

Our broody BR hen has spent the last 25 days (or so) on the nest.  She has been very faithful to her project.  Yesterday, I put a low board across the floor of the coop, to act as a partition that would keep the poults from falling out the door of the coop, because I don't think they could get back up the ramp.  The hen got up for lunch and a stretch, but then she stayed in the yard.  Finally I decided that the board (which was obscuring her view from outside) was confusing her.  I took it out, and she promptly went back to the nest. 

She was off the eggs for an hour.  Maybe two.  As soon as she was back on, I reached under her, and felt an egg.  It was cool.  Almost cold. 

Did I ruin the hatch by putting that board up?  Is there anyway to tell if the eggs are still kicking?  I candled one, and I saw that it was very well-developed (all dark, except for a good air-sac).  I'm anxious to find out if they are still viable.

Thanks in advance for the help!

(edited to fix typo) (edited again to change title of thread, because no one was replying and I couldn't stand it!)

As of last night, no hatchlings. Today would be on the early end of my estimate for 28 days, however, so it's to early for me to make any predictions.

Last night, she was much more protective/defensive than she has been. Previously, she was pretty docile if I reached under her or stepped over her to fill the feeder. Last night she bristled and hissed as soon as I got near. Does that change in body language mean anything to any of you?

Thanks!

Thanks, everybody. 

Another question: in the event that the next few days come and go and no little poults arrive, how long should I leave the hen on the eggs?  If the eggs aren't viable, I don't want her to waste away on a futile project.  On the other hand, if I got my timing wrong, and they actually just have another day or two to incubate, I would hate to take almost-hatched eggs out from under her. 

I'm trying to prepare myself for the possibility that there might not be any baby poults coming out of this.  If that's the case, will she generally know when it's time to give up on them?

I am surprised at how anxious I've allowed myself to become over this.  I have to fight back the impulse to be constantly poking her and asking: "have you hatched any babies yet? ... what about now?  Now have you hatched any babies...?  What's taking so long?... how about now?..."