While those are great reasons to “worry” about time, that’s putting the cart before the horse. One thing I always hated about my life drawing classes, especially when I first started out, is we only had about 2-5 minutes to draw a pose. While this is fine for gestural work, it taught me nothing about anatomy. I had to go learn that on my own, even though I had the best reference sitting right in front of me, I never got to utilize it, because of the time restraints the teacher put on us.
That’s why I am not a big fan of speed challenges for those starting out. Time is quite important for the professional, so in the work environment you need to worry about, deadlines, etc… If you don’t know how long you need to sketch tells me this person isn’t ready for that type of work yet.
Speed doesn’t mean anything if you can’t produce quality work. Quality work comes from practice, which leads to faster working time. You can’t start out being fast and have quality work. It’s like putting the cart before the horse.
So like I said before, why worry about time? And to be quite honest, I never worry about time. By experience I know what I can do, and when I can do it. This fellow doesn’t know how long to take, so I am saying for him to practice, and learn on his own. Telling him 25 minutes, or 5 minutes doesn’t really help him out. Having him pick up his pencil and see for himself is the only way for him to “truly” know how long it’s going to take him.
My opinion of course.