def time_claim(name)
      claim = self[name]
      if claim
        begin
          Time.at(claim)
        rescue
          raise Sandal::ClaimError, "The \"#{name}\" claim is invalid."
        end
      end
    end
def time_claim(name)
      claim = self[name]
      if claim
        begin
          Time.at(claim)
        rescue
          raise Sandal::ClaimError, "The \"#{name}\" claim is invalid."
        end
      end
    end
Gets the value of a claim as a Time.