Drip feeding during tempering

Hey,Firstly just to introduce myself I'm Rowan and I've just started a really small chocolate company in London, this forum looks excellent, it's really good to talk to so many people who are doing the same thing. So far everything has been going really well, we've had some problems with kitchens etc but everything generally seems to be falling into place.My main question right now is about tempering. I know everyone talks about it a lot but I can't seem to find the information I'm looking for. We're currently using a chocovision machine to temper all our chocolate and it's working fine but we find ourselves needing to temper more chocolate so I've been researching and found out about the 'drip feeding' method. From what I can gather you temper some chocolate and then you can remove some of the tempered chocolate and add the same amount of untempered melted chocolate and overall the chocolate in the machine remains tempered?? This seems perfect for us to increase our output a little! I was wondering though how much chocolate can you remove and add to the machine in one go for it to remain tempered - say 20%? Also after adding the untempered chocolate do you have to wait for the crystals to form, if so how long will that take?Any help would be fantastic Rowan