How to adjust stewing time for different weights of meat? Simple scenario: I've got a Madras recipe that tells me to stew 2.0 kg of Lamb shoulder meat in the oven, covered with foil for 2,5 hours at 180 deg Celsius, then another 30 mins at 200 deg without the foil. 

Now I'm cooking for only a few people, so I have 0.6 kg of meat, i.e. only 30% of the recipe's weight. 

So, my question: How should I adjust the cooking times? Any useful rule of thumb?

My initial thought was be to factor times down to 0.6 / 20, i.e. respectively 45 and 10 minutes. Then again, this seems on the low side for a tender stew (or is it?). This is probably because of those 2,5 hours, maybe 50% would be to ensure the meat's cooked, and the other 50% is to ensure it's tender; and those halves are to be adjusted differently?

Suggested questions "that may already have your answer" has one great title, but question nor answer helps me answer my question. Searching seems to yield zero results, though my queries may've been wrong.
With lamb (and stews in general) it's not a great idea to adjust cooking times to account for quantity of meat. I have found some useful information on this Chow.com article:


  The key to cooking any tough cut is slow simmering over low heat—lamb shoulder could take upward of two hours to reach the tender zone. Don't be alarmed if the meat seems quite tough after it's cooked for a while, sunshine842 says. The muscle fibers seize up, then relax into a state of tenderness after more cooking. Just keep simmering.


So if you reduce your cooking time to 30% then the meat will have 70% less time to relax and become tender. I suggest to instead stick with the original cooking time and just check it now and then. You can't really over-cook shoulder over low heat.