Md. Code, Election Law § 15–105

(a) For principal political party candidates, the qualifying period is from the first day of the election cycle for a gubernatorial election until the first Monday in May, inclusive, of the election year.

(b) For all other participating candidates, the qualifying period to qualify for only the general election is from the first day of the election cycle for a gubernatorial election until the first Monday in August, inclusive, of the election year.