Yeah, I increase my time as well because it frustrates me when I'm not even able to complete each piece or I'm not satisfied with it.
I think it's a good practice with people who focus on details a lot (I'm that person) so the 30 secs are to help them not to get stuck on one part of the body and be more flexible.. but I think increasing the time, in the beginning, helps to get used to sketching gestures and then once you're more comfortable and know what's the process that works for you (like @Lockenheim said) you can then start decreasing the time.