Still I think it's really good practice to to try to quickly think of all the variables required for a good compo / painting - hues, temperature, composition, light, hard & soft edge, depth, weight and so much more.
I see these dailies as just sorta sprints to prime my brain to think quickly through the problems that I have already practiced thinking about in longer drawn out artworks though. Done on their own, they would probably have the terrible effect of inculcating a shoddy habit of mindless quick painting.
It's a skill to work methodically with precision while still doing so fast. Setting a time limit for a painting like this should be done purposefully as a side to the real practice of creating art where one has all the time needed to work out and ruminate on all the nuances of a piece. One naturally gets faster at it in time anyway.