From the good people at mypetchicken.com:
'"Egg discard" times have not been tested for this wormer, and this is THE one wormer approved for use on chickens. The reason drugs are so seldom labeled for use on laying hens is that drug companies don't see a return on their research dollars when it is more cost effective for factory egg farms to simply slaughter sick chickens and buy new healthy ones. Keepers of backyard pet chickens don't want to do this, naturally! We don't see our pets as egg producing machines to be discarded when they "break"--in fact, for backyard hobbyists, it's usually all about saving a beloved hen's life, and not about the production of eggs at all!
Although this medication is also used to treat humans, it has not been tested for withdrawal or "egg discard" times your chickens, and so cannot be labeled for use on laying hens due to the fact that how long and how much medication could be transmitted through the eggs is unknown.'
Seems to me it's nothing to worry about.