The authentication and authorization system used with OneDrive for Business is Azure Active Directory (AAD), which has different expiration times. With AAD, any single refresh token is valid for 14 days. Every time you redeem a refresh token for a new access token, we also provide a new refresh token that is good for the next 14 days, so you need to store both the new refresh token and the access token each time you redeem a refresh token.
Beyond that though, AAD has a requirement that users log back into your app every 90 days. Thus, you can extend the 14 day refresh token expiration by requesting a new one multiple times, but after 90 days you have to go back through the sign-in experience.