While many Americans are worried that real estate prices have flattened and may even turn downward, some of the country’s top commercial developers say there always is opportunity for those who manage their projects efficiently in a global market, focus on areas with growing demand and have the staying power to wait out the downturns. After record growth in 2006, how does the commercial market look today? “Let’s just hang on and hope these times continue,” said William L. Mack, referring to the current era of low-interest rates, rising rents and soaring real estate investment. Mack is managing partner of Apollo Real Estate Advisors, a New York-based real estate firm with office, retail, hotel and other projects in 20 countries. Investing in commercial real estate hit a record $306.8 billion in 2006, up from $276 billion the year before, according to the National Association of Realtors.…