Never ask for more than 15 minutes of the prospect's time. Fifteen minutes is a small price to pay for an idea--and 15 minutes is easy to manage. The prospect can fit you in between other appointments. Fifteen minutes is a coffee break. Anything longer, and most busy prospects imagine their day eaten away by your presentation. Remember, the prospect's time is valuable.
You can easily complete a standard proposal in 15 minutes. In fact, if it takes longer than that, it's usually because the prospect is very interested and asks a lot of questions.
Excerpted from Creative Selling: Boost your B2B sales