hmm...It doesn't seem to be working here.
I tested in the following scenarios:
1. Minilyrics found the lyrics while MB didn't find and said "unable to find any lyrics" without refreshing the window automatically
2. Minilyrics found synced lyrics while MB found only unsynced lyrics and displayed it without refreshing the window automatically
3. Track already had unsynced lyrics embedded and Minilyrics found synced lyrics but MB only displayed the unsynced lyrics without refreshing the window automatically
I believe the polling is done automatically when only Minilyrics is active and not by enabling an option
You may need to increase the polling time because searching 5 lyric providers it takes more than 10 secs on my connection(2mbps). While it searches through all providers it should poll in between so that the lyrics will be displayed quicker than waiting till it searches through all providers.