The first exercise is to draw a particular object several times, each time a bit faster. The first time 3-4 minutes, the second in 2 minutes, 1 minute, 30 seconds, 15 seconds, and then 5 seconds.
Looking for that happy medium where my drawings retain some substance but are still doodles... I'd say usually 30 seconds to 1 minute.
After I doodle my way into something amazing, I'd like to print my work on cards, perhaps journal covers, and maybe small posters. We'll see.