In an effort to make it look, well, effortless, dancers with the Boston Ballet spend as many as seven hours a day in practice. During weeks when they are not performing, a typical day begins with “company class” at 9:45 a.m. in their South End headquarters. Dancers, like Heather Waymack (left), spend 45 minutes doing barre work and warming up. Another 45 minutes is devoted to “center work” where dancers start with small slow movements that build in intensity, speed, and difficulty. Says Jo Cardin, a spokeswoman for Boston Ballet, company class is designed to build skill, technique, and flexibility for the day ahead.