Any time i've been sent something from the USA by Airmail it always taken at least 7-10 days to reach me here in the UK.Bought something a few weeks back from ebay the seller was in the states & got it a week later.
Actual personal mail from the USA to the UK generally takes 5 working days. Commercial mail would need the 5 days for shipping plus however long it takes the company to get its arse in gear to send your goods. If it takes them two days to process your request and stick it in the mail, then you should expect it to take 7 working days. But some companies can take weeks to process your order so it's entirely dependent on the speed of their capabilities.