One minute after the 6:45 p.m. listed starting time for “The Hangover Part III” at the AMC Loews Boston Common, a half-full theater darkened and fell silent except for the crunching of popcorn. The ads came first. Then that familiar green light bathed rows of upturned faces.
“The following preview has been approved to accompany this feature by the Motion Picture Association of America,” flashed on the screen. Twenty minutes and seven previews later, the featured film began.