ACP are instituting a new process for BRMs this season. It has the potential to speed things somewhat.
If an organiser sends in his results very promptly and if both validation sec and the recorder are sat waitng by their computers instead of out riding their bikes, and if the new automated ACP process works as intended for BRMs, then the whole thing could, in theory, be complete on the AUK website in about a week.
That's an awful lot of IFs though, and in reality I doubt you'll see many approach that sort of speed.
Getting the cards back to the riders will always take a little longer due to the necessary reliance on snail-mail from validation sec to organiser and from organiser to rider.
Personally I rather like it when a card comes back months later.... memories of any pain have faded and I only think "gosh - that was fun ride wasn't it, nice to be reminded of it". And I'm not saying that because I'm an actor in the process (honest!)