When to greet a customer in a retail setting

The BusinessWeek article How to Win Frugal Consumers and Influence Them to Buy highlights shopping behavior researcher Paco Underhill's retail guidelines:

• Shoppers use the area just inside a store's entrance as a decompression zone. They won't notice signs put there.
• Americans naturally turn right as they walk further into a store.
• Customers respond best when employees greet them about a minute after they enter.