line confidence with me came from just drawing over and over so it could also be improved over time with 30-second gesture as well. do whatever works for you best or experiment and find out what works best didn't mean to influence you to go for a longer time if you were fine with what you were doing before. basically, line confidence is what comes out of trusting your brain, eyes, and hand to correctly make the line the fits what you are drawing at least to me. That comes with time as you draw more and more so if you thin 2 min. will help go for it.