Md. Code Ann., Tax-Prop. § 14-808

(a) (1) Except for property that has been transferred by a municipality or county to a land bank authority established under § 1–1403 of the Local Government Article, and except as provided under § 14–811 of this subtitle, the collector shall proceed to sell and shall sell under this subtitle, at the time required by local law but in no case, except in Baltimore City, later than 2 years from the date the tax is in arrears, all property in the county in which the collector is elected or appointed on which the tax is in arrears.

(2) The collector is required to sell, but failure of the collector to sell within the 2–year period does not affect the validity or collectability of any tax, or the validity of any sale thereafter made.

(b) In Calvert County the collector shall proceed to advertise and sell any real property immediately after the tax is delinquent for a period of 1 year.