I think you need 5-6 days. D1: Chengdu, D2: to Qingchengshan in early morning and get back to Chengdu the same day; D3: to Leshan and to Emeishan in the afternoon, stay one night in Emeishan, D4: take bus to Zigong. if you do not prefer a stopover in this place, change bus to Dazu, D5: get back from Dazu to Chengdu before 5pm. The last bus back to Chengzu is at 5pm. Get to Dazu bus station earlier. 5 hours later to Chengdu.