The idea behind requiring quick action on someone's part is to exploit the emotional impact of a demand so the person who is being backed into a corner doesn't

The idea behind requiring quick action on someone's part is to exploit the emotional impact of a demand so the person who is being backed into a corner doesn't have time to think and just reacts to remove the pain. Without a time constraint people end up gathering information, and getting over the psychological shock that clouds judgement. A somewhat similar concept (not related to this) is the idea that "time kills all deals". The more time goes on the less likely a deal will occur.