The status and last_touched postmeta for clone events is not reset properly.
For instance, if Event A has been tweeted in the past, and I clone it into Event B and set a new time, it will inherit the status and last _touched postmeta of it's sibling. Event B will never be reset to pending and will not be tweeted.
I've also seen a case where these key's values are blank and are picked up for the queue but I have not found a way to reproduce.
This idea has been addressed on the new timely web application. Try out during private beta at https://www.time.ly/new.
All plans are FREE during private beta!