We'll be using FacebookConnectRequest in our games, and I've checked Facebook's documents regarding to access token usage. After reading those documents, some questions popped in my mind. I've looked at previous entries for the subject, but couldn't find exact answers so I'm shooting this.
We don't refresh the token manually. The users details will get refreshed when they use the FacebookConnectRequest with a valid token. At this point the displayName will be synced or updated (if specified to do so) and any friend list changes will be applied. These changes require players to authenticate via Facebook so their details can be refreshed. We only sync the displayName and pull in the relevant friend details during this process. I hope this helps.