So I’d agree with the first point on consistency, but I’d slightly disagree on the fast times comment.
Sometimes, tuning the kart is what helps the driver to get more comfortable to push in different areas than they might otherwise.
My philosophy is that as long as the driver is consistent, even if they are three seconds off the pace, we can do some tuning knowing that the driver will remain the same.
Just telling them to go faster until they hit a ‘tuning laptime’, doesn’t make any sense to me, in my opinion.
What I would recommend is having a driver’s notebook with you, so that you can take notes on your driving. (I’ve written an article about what things you can include in there here: https://startinggrid.org/2011/07/30/want-to-track-your-improvement-get-a-drivers-log/
I’d also have a tuners book for your kart, so that you can get used to making small changes, and seeing what handling differences you notice. If you don’t get any experience with it, it won’t matter if you start tuning once you “reach the fast times”, because you won’t know what the kart does. Get experience with it now, and like seat time, put those files in your mental folder.
Here is a link to some examples of some setup guides: Let's Build the Ultimate Kart Setup Sheet
Finally, here is an article about how to better plan test days, so you get more out of practice: https://startinggrid.org/2016/01/12/kart-tip-how-to-have-a-more-effective-practice-day-theartofkart/