I'm not sure what "2/5 Portland" stands for. O.C. however stands for "Order in Council". As it relates to Loyalist land petitions it means the date that the Order in Council was issued approving the petition.
In order to be eligible to receive the land that a U.E. Loyalist or the son or daughter of a U.E. Loyalist was entitled to, the petitioner had to have reached the age of majority (21) or be married. This has led some researchers to interpret the O.C. date as either the 21st birthdate of the petitioner or the marriage date of the petitioner. It is synonymous with neither. It is simply the date that the Order in Council was issued, nothing else...regardless of what you might read elsewhere.