If one chicken gets into something, generally all of them do. A molasses flush for 4 hours won't hurt them but may indeed help them. I'd go ahead and do the whole flock.
Something I do (because I know the molasses flushes toxins from their bodies) is feed Wet COB. That is Corn, Oats, Barley with molasses. I add that and dry cat food to my daily feeding of lay pellets. To 3 scoops of lay pellets, I add one scoop of COB and one scoop of cat food. Each bird ends up with a very small amount of the cob and I "believe" it keeps things functioning well. I've been feeding this for almost 2 years now and have had no incidences that would cause me to change. They still get digestive upsets from time to time but hey, they're chickens! I fret over them pretty bad when they get sick and baby them through it til they're back out in the flock.