Maryland Code, Election Law § 10-309

(a) In accordance with instructions provided by the election director, an election judge shall arrive at the polling place and, under the direction of the chief judge, set up the polling place to assure that the polls will be open and operational at 7 a.m.

(b) Except as provided in § 10-303(d)(2)(ii) of this subtitle, an election judge shall admit an accredited challenger or watcher one-half hour before the polling place is open.