I got a rx on 5\6 for oxycodone 30 mg. What day can it be refilled at 28 days or at 31 days?

It is really up to your doctor. Federal law says that you can fill another script for a controlled substance in 28 days from the day the script was filled. Count the days with the day the script was filled as day one. Now I have had, in the past, one doctor who I would go see for my pain meds. I would see him every 4th Thursday (or on the 29th day), He would write me a script and then tell me that I could go fill it that day. The previous doctor before him told me that I could fill my script on the 30th day. But the doctor I now have, make me wait until the 31st day before I can fill my script for my hydrocodone. Although the feds says it can be 28 days, it is really the doctor that is giving your pain med scripts to you whom decides how often that you can take those scripts to be filled at a pharmacy (that is, taking into account that the script is within federal guidelines). So be sure that you understand the refill policy for the doctor you are seeing. Because if you try to fill a script from a particular doctor too early, then you could run the risk of being kicked out and that doctor's practicw, then he would no longer write you scripts for the pain meds you need. And it is very hard to find a new pain management doctor who will prescribe the right pain meds that work well for you for your pain control.

Your appointments are 4 weeks apart, I would assume your prescription is for 28 days. However many it says to take a day, multiply that by 28 and that should be the total prescribed. If the prescription is for more, multiply the daily dose by 30 to see if that's the correct total. When your pharmacy is open or closed has no impact on the number of days. Or you could always ask your doctor or pharmacy.