[Exim] Exim usage dependent on time of day

Hi,

Is there any way to control the load that exim puts on the network trying to
deliver messages based on the time of day. So that night time use could be
higher than we might want during the day.

I would like to do something like:
    queue_run_max = 50 at night
    queue_run_max = 50 during the day

TIA

--
Alain Williams