This behavior is likely on the OneDrive side. Okta just does the authentication. The remaining behavior is typically determined on the OneDrive side.

If accessed through a browser, there are two sessions: a session for Okta and a session for OneDrive. If the session for OneDrive ends, you'll need to authenticate with Okta again to create a new session for OneDrive. If you're not logged into Okta already, you'll likely be prompted for credentials from Okta again. If you do have an active session with Okta, then you'll probably be automatically authenticated and SSO into OneDrive.

If this is from a rich-client, then Okta likely has no involvement in the session time and is just fulfilling authentication requests.

In summary, check what the session time is for OneDrive.

But if you do need to check or change the session time for Okta, then go to your admin console and head over to Security > Authentication > Sign On, click the pencil icon to edit a rule, and there will be a configuration item for "Session expires after".