The St. Charles Singers, led by founder and music director Jeffrey Hunt, will open its 41st concert season with “Time to Explore,” a program that illuminates how classical composers have availed themselves of folk melodies. “Some of these works are rarely heard anywhere, and all but two are new to the St. Charles Singers’ repertoire,” Hunt says. “It’s the start of a season filled with musical discoveries that our choir will relish and that will surprise and delight our listeners,” Hunt says. “Time