"Because this is an important problem, I would like a response as soon as possible." "I would appreciate your speedy response." "I want to hear from you as soon as possible." "I look forward to hearing from you as soon as possible." (A little old-fashioned.) "As soon as possible" means within one business day. If you don't get a reply within one day, follow up with another email. It's best to call your customer service department if you need to make an urgent request for a response time frame. Most companies will try their best to meet these requests.