Each business owner gets to choose the length of time a customer has to enter their receipt code or scan the code for points. Typically this amount of time is printed on the receipt just above the QR code.
QR code scanners and alpha-numeric code enterers have the same amount of time to use the code. If you miss the window and didn't get credit, please send a picture of the receipt to firstname.lastname@example.org and we will be happy to credit your account accordingly.
Receipt code expiration is a security measure in place to protect business owners from scan fraud (for example, a user finding a bunch of old, unscanned receipts in the recycle bin and scanning them for points).