Purchase challenge?

I have attempted to purchase from Dell earlier today. 

My credit card checked with me and I have confirmed my intention to purchase and my card shows as "verified" on the Dell website.

I have now spoken with my credit card company and they have confirmed that they have given the government ahead to Dell to complete my payment but nothing has happened.

I have called Dell sales and they advise to wait for the payment to clear.

How long should I wait? 

It's now been around six hours since my purchase was authorised by my card provider?