It depends what specific antibiotic is being used. Some have no withdrawal period, others have long withdrawal periods. There might be some that eggs may not eaten at all...forever.
You're right. I've seen worm resistance with ivermectin in poultry. I rotate wormers.
As far as antibiotics go, if chicken owners practiced strict biosecurity, you wouldnt see half as much threads in the Emergency/Disease/Injury forum.