Forum Discussion
Migrate from Federated to Password Hash for Office Pro Plus
If you deploy Seamless Single sign-on as part of PHS, then it is more than likely that you will not see any problems with users being challenged for credentials once the switch has taken place. However, this cannot be absolutely guaranteed i'm afraid. The behaviour of O365 Pro Plus in these situations is almost impossible to completely predict.
Deploying the URL's for SSSO should help though. You can read more about this here - https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sso-quick-start
Just remember that your users O365 Pro Plus clients will be at different stages of the 30 day call home to do a licence verification cycle.
Edit, just noticed this is a very old post so guessing you got this sorted out.