Homeland Security Overtime Reimbursement Act - Amends the Omnibus Crime Control and Safe Streets Act of 1968 to authorize a recipient of a grant under a homeland security overtime program (i.e., a program for which a grant is made to fund overtime expenditures to law enforcement agencies for training and increased patrols related to homeland security concerns) to use grant funds to pay for homeland security overtime expenditures incurred during the fiscal year before the grant is made. Directs that: (1) the Attorney General waive the requirement of a nonfederal contribution for any portion of a grant used to pay for such expenditures; and (2) Puerto Rico be considered both a unit of local government and a state for purposes of such a program.