I taxed a Mercedes first thing Saturday morning and it took until yesterday (Tuesday) to show, did a Mini earlier and still not showing.
I print out the confirmation page and give it to the customer now. At least they can see its been paid.
As for sending of the V5's I wait until I've got about 10 and send them together but stick 3 1st class stamp on the envelope to make sure they get there !! Would cost me more in fuel to drive to the post office!!!