Wholesaling Assignment Contract Questions

[Megan Elise McIlvaine]

Alright, I've got two questions for you all.
1: When I send over the Assignment contract to be signed by my cash-buyer should I set a time for them to get it back to me signed and if so how long after?
2: Is it considered rude or not proper wholesaling etiquette for me to have two cash-buyers who both have been given an assignment contract by me and informed that the first to send it back to me signed will get the house? Of course I would return the earnest money to the cash buyer who returned it second. 
Thank you, any advice or knowledge acquired through personal experience is appreciated!