It runs at the next opportunity it gets after
the scheduled run time. In your case, it ran on Tuesday last week at 6:14 pm (that answers the "So is it not synchronizing on it's own
?" part. Your clock synchronizes every sunday). If you could remember that it wasn't synchronized back then, it might have gotten an error but task scheduler still reported it as successful. Personally, I had my issues with synchronizing with time.microsoft.com.
On another note, there really is no need to synchronize your clock more than once a week. If your clock really gets that off often, then I would follow jumanji
's advice since that's most likely the culprit. The other possibility is that some program with admin access is messing with your clock.