I think Culpeper is right: on or off. But you can set your third party updater for lauching the avast! iAVS4 Control Service:

C:.…\Avast\aswUpdSv.exe

You must disable the automatic starting of this Service (Administrative Tools > Service > avast! iAVS4 Control Service > ‘manual’). This way you will be able to set the delay after the connection is established for the updating.

If I’m wrong, it will be a value for configurating this here. 8)