I ask for payment within 5 days although I would extend that if the buyer requested it for a good reason.  

Having said that, most of my buyers pay immediately or within 24 hours of the auction's end. 

It also depends on what the buyer asks for.  Some set up their items for immediate Paypal payment only, and some are happy to wait a week.  

I think the sooner I can pay the sooner I get my item!