In my opinion it depends on the other person and the product you sell. If he knows the product or not, if you are going to have a long term relationship or if he's going to buy once... You will know it with the feedback you receive from him/her. If the product is very technical or simple,... For me, is the necessarious time I use to make the other person to understand what I wanted him to know about the product. So, you can't be looking at your watch and thinking about time. Or if this person is going to make a huge purchase... who cares about time??? Show him the product, explain it, take him to do a mini-tour in your city, invite him to have lunch, dinner,... whatever!!! But make him buy!
