In less than 30 seconds, three robbers armed with a handgun and a hammerheld up the Tourneau fine watches store at King of Prussia Plaza inUpper Merion. The blink-of-an-eye haul that included simply smashing oneglass display and stealing 18 Rolex watches: $576,000.“It happened simultaneously,” Upper Merion Police Sgt. Jeffrey Maurersaid of the heist that happened at about 8:45 p.m. Wednesday. “One maleheld up some shoppers and an employee and told them to get on the groundwhile the other smashed the glass. It all happened in about 20 to 25seconds, all very quick, in and out.”Maurer said the watches are obviously very expensive, but investigatorsare more concerned that the robbers came armed with a handgun. He saidthey have had smash-and-grabs before, but this “was an armed robbery.”The three suspects, who have yet to be identified, were caught oncamera, and the hammer was left at the store. Investigators have yet todetermine if this robbery is connected to other similar crimes inLimerick earlier this week and a heist in Cherry Hill, N.J.