# File lib/ice_cube/validations/minutely_interval.rb, line 30
      def validate(step_time, start_time)
        t0, t1 = start_time.to_i, step_time.to_i
        sec = (t1 - t1 % ONE_MINUTE) -
              (t0 - t0 % ONE_MINUTE)
        minutes = sec / ONE_MINUTE
        offset = (minutes % interval).nonzero?
        interval - offset if offset
      end