It seems like there is no way to break out of a sync loop.
I'm using the Daytime protocol to fetch time from a time server. Obviously, the fetch could fail due to any number of Ethernet issues. I have included timeouts in my code to prevent infinite loops when fetching the time. But it appears that this is not the case in the Time.h API. If I call setSyncProvider() and set the setSyncInterval() to say 60 seconds. I let it sync the clock the first time. I pull the Ethernet cord out and wait for it to re-sync. When the 60 seconds expires it continues in a loop and appears to never end.