As long as the packs are left selected 'on'when the final shutdown checks are done,then the next apu air 'on' selection will start the packs in a 1 then 2 delayed sequence(10secs).. .My outfit used to select the packs 'off' at the end of the day,the early morning start up was a tedious on & off rigmarole,until the temps equalised.. .Airbus'told us that with the "new" software the packs should be always left 'on',this has cured it for us in most cases.