The Zoning Board of Appeal on Tuesday approved the Pot, a marijuana shop proposed for 532-542 River St. in Mattapan Square. The shop, which won approval of the Boston Cannabis Board in October, now goes to the state Cannabis Control Commission for the last major approval it needs before it can begin. Applicant Dru Ledbetter, said the store would be open 10 a.m. to 8 p.m.