I'm allowed to hang out ---friends---Sunday afternoons.A:wit

D hang out with friends hang out with sb.是固定搭配,和某人一起闲逛
in 用在“年、月、季节”,在早晨,上午,下午,晚上,或一些固定短语中.如 in spring,in the morning
on 在某一天,或某一天的上午,下午,晚上
on Sunday,on Mother's Day,on the evening of June 1st
所以是on Sunday afternoon