def background_queue_start
      env = environment
      return unless env
      queue_start = env[:queue_start]
      return unless queue_start

      (queue_start.to_f * 1000.0).to_i
    end
def background_queue_start
      env = environment
      return unless env
      queue_start = env[:queue_start]
      return unless queue_start

      (queue_start.to_f * 1000.0).to_i
    end
Returns calculated background queue start time in milliseconds, based on
 environment values.

 @return [nil] if no {#environment} is present.
 @return [nil] if there is no `:queue_start` in the {#environment}.
 @return [Integer]