That is the whole point, the user doesn't have to know, he says to submit the file and to all intents and purposes they have because avast takes care of it for them.
The detection might happen when the user is off-line (we all aren't on broadband and or always connected) and then you are forced to wait, as we both know avast doesn't establish a connection but checks for one, so for me the logical place is in the update process (or you have to include another process solely to handle submissions).
IMHO, they doesn't really need to know the policy (but the help file could outline how it works), but even if they know the policy there shouldn't be any need to have a choice send now or later. avast has one constant, the update process which personally I feel is fine as it is connecting to the avast servers at that point, the connection has been established.