How long do I wait to follow up on a pitch?

I have a question about a timely pitch I just submitted last night. The head editor cc’d me as he passed it on to the foreign desk for review. My questions are: How long do I wait to follow up? And do I let them know I want to pitch it elsewhere? (Or are these things assumed? And if I don’t hear by mid-day today, should I assume they have passed?) 

Reply right away and say thanks, and that you’ll need an answer by [DATE/TIME]. That date/time should be just before you think the piece will “expire"—and give you enough time to send it elsewhere. You can be up front with the editor and say that if you don’t get a reply by DATE/TIME, you’ll have to take the piece elsewhere because the hook is going to disappear. 

I think editors generally appreciate an up-front convo about these things. It’ll help him push the foreign desk for a faster answer, too.