An employee in or under an Executive agency who is a veteran of a war, or of a campaign or expedition for which a campaign badge has been authorized, or a member of an honor or ceremonial group of an organization of those veterans, may be excused from duty without loss of pay or deduction from annual leave for the time necessary, not to exceed 4 hours in any one day, to enable him to participate as an active pallbearer or as a member of a firing squad or a guard of honor in a funeral ceremony for a member of the armed forces whose remains are returned from abroad for final interment in the United States.