Is there a 3 day grace period on filling Adderall?

You might want to add a qualifier; e.g., before OR after xxxx where xxx can be something else you know better than I. :-) where 'xxx' may be: a) vacation, b) requesting a new script, or c) refill a lost/stolen drug.
My experience is that I can fill a script for about a year after which the script becomes invalid. Pharmacies will usually keep a FILLED script for somewhere between seven and ten days AFTER you request a refill in the active bins. After that the script's content returns to inventory. You can always ask to get a refill as long as the script has not expired.
If you are asking about getting a refill BEFORE your current refill has expired, you can request a vacation override. I have usually had no problem getting them as I have been going to the same HMO for more than ten years. If you lost a script, just ask for a new one or check if the pharmacy has that script on file. If you lost a drug, depending on its classification, have a good reason.
All "bets are off" depending on the type of drug or medical gear; e.g., opioids, needles, and equipment for transfusions and dialyses.

I know insurance companies will let you fill prescriptions 5 days early on an occasional basis. If they deny you the pharmacy won't fill it even if you offer to pay cash.