They usually err on the side of caution, so many will give longer recommendations. Some vets will say that with Baytril (enrofloxacin) you can NEVER eat the eggs again. I think most people follow a 2 to 4 week withdrawl with most medications, many do not have vets recommendations available. I would do what you feel comfortable and safe with. There is no point in making yourself worry. If 8 weeks is comfortable for you, then follow your vets recommendation.
Sulfamide antibiotics are not approved for poultry in any country in the world due to growing antibiotic resistance, so there are not many studies being done on egg withdrawal times for chickens. This is an older study that says that 10 days after stopping the sulfa drug should be long enough. https://www.ncbi.nlm.nih.gov/pubmed/1476095
Zombie thread revival, but I happened to run across this thread and this new article from 2021.
This suggests 43 days withdrawal. Ouch. If you click the link for open source manuscript the methodology can be reviewed. That said, the FDA calculations are opaque to me and the authors do note this is 'likely' conservative. Especially if I'm interpreting the level of detection comments.
Many people here on BYC used to use Sulmet (sulfamethazine) to treat for coccidiosis, before Corid became more popular as a first line treatment. The old warning here was that you could not eat the meat until after 10 days, so many used that as a withdrawal time. It has never been approved for egg layers, but most people just waited a certain amount of time. A month is fairly reasonable time for most medications, but you probably won’t find a recommended egg withdrawal time from any official source. FARAD is the official source in the US to consult. Only a few medications are approved for poultry, and sulfonamides are not. You can do some googling for yourself.
Interesting, and as good as google is, it's nice to review the primary sources. I didn't save the links but there was one mid to late 20-teens that was a precis that FARAD put out. Noted most commonly requested medication information and the trimethoprim-sulfamethoxazole was in the top 10, and not enough data at that time other than contact them directly. No generic guidance.
Another article I did not save noted the difference in clearance between different sulfa drugs, so data for one could not necessarily be extrapolated to another. Thus whatever was true about sulfamethazine would not necessarily be accurate for sulfamethoxasole.
But, as you say, these are not approved for poultry and there will be little $$$ thrown at the questions.