Erythromycin has a 24-hour withdrawal period.
General advice:
There should be a withdrawal period on the bottle. If there isn't one, it wasn't tested on poultry or your have the non-poultry-specific supply of the active ingredient. If the former, you probably shouldn't use it except as a last resort. If the latter, look up the type that is used on poultry and double-check to be sure you're actually using the right dosage.
An unprofessional rule of thumb is that you should ignore the "do not use in birds producing eggs for food purposes" bit because they will never come out with a product meant for use in egg-laying hens. Big egg sellers don't keep their hens for long enough to have to medicate them, and so no products are tested in egg-laying birds. Not enough demand=not enough funding=no product=use your own good judgement.
Erythromycin Brand Name Gallimycin water soluble powder is used as an aid in the treatment and control of chronic respiratory disease and infectious coryza. Also for use as an aid in the management of complex disease syndromes such as bluecomb and synovitis and in management of respiratory outbreaks and syndromes resulting from the stresses of movement of birds.
Active Ingredients: Each gram contains Erythromycin (as erythromycin phosphate) 231.2mg
Dosage: Use as the only source of water for 7 days.
Cure: For small birds (finches, Parakeets etc.) use 1/8 teaspoons per 2 quarts of water. For large birds,Pigeons to Macaws and chickens, Cure: 3/4 teaspoons to 1 quart of water.
Note: Medications should not be given when chicks are in the nest. Treatment to birds while sitting on eggs is okay before the eggs are hatched.
Warning: Treatment should not be given if you use the food or eggs for human consuption for at least 24 hours after the last treatment with this drug. Do not use in birds producing eggs for food purposes.