I started a Character-Design-Mentorship with Anthony Jones. The first assignment was to design 20 thumbnails for a universe of our choosing.
I went for "Sci-fi-bounty hunter" and did some studies for that.
What was new to me, was the idea of using a timer while doing studies ... while working generally. So most of the studies were done in 5 minutes.
What it does for me is to keep me focused on doing them efficiently and to not go on "auto-pilot". The latter was a problem for me usually, especially when doing longer studies.
I simply use the Watch-App that is native to Windows.
After doing the thumbnail sketches I switched to another idea, which I will show next time.
Until then, happy learning.