No, it isn't too late. I prefer DiMethox or Sulmet though. Corid is a thiamine inhibitor. While you usually don't see any problems, it can cause problems like polio. You can always give B Complex shots after treatment.
Isn't to late at all. If you suspect cocci, treat them. I use corid without issues, but, if you want to give a fortified vit B complex shot or Thiamine shot after, you can do so, if you fear Polio. Give proper dosage, you should be just fine.