It is not possible to set an Expiration Date (the deadline for access) on QR codes generated by Teachme Biz's features.
If the Manual linked to the QR code becomes inaccessible due to deletion, Archive, Unrelease, or similar status, the Manual will also become inaccessible via the QR code.
Related: Outputting a Manual QR Code
https://teachme.jp/8/manuals/5619038/