Hi, I know this is an older post but I want to get back to these forums and would like to share my thoughts on this subject.
My first point I'd like to point out is you will never stop learning. If your doing characters you will struggle with poses forever. The human figure has a near infinite pose potential. Mastering every angle is a huge task and one that takes a life time.
However, to speed up your drawing time I would suggest doing gesture drawings for 30 min's to warm your self up. Drawing cold leads to longer drawing times. Warming up also helps you get into the drawing mood and lets your brain shift gears to the artist side easier.
As far as time goes I break it down to sections.
1. Anatomy and Pose - This part I'd say is 90% of the work and can not be rushed.
2. Clothing and Details - This part I'd say is 8% of the work and is the fun part.
3. Light / Shadow / Color - This part is really the final 2%
In terms of time there's a major difference in drawing thumbnails and getting a final render. Thumbnails need to be created fast and this is what you show your clients to see what they like and what they want for a certain character. The turn around pose is some thing you'll have to learn to do quickly. However, the final render based on the turn around drawing is where you spend your final time.
To create a character it can take days, weeks, or even months before a client feels like the character is done. Now for your portfolio work, I would say come up with a concept and spend a week or 2 weeks on one character until you feel you have hit the nail.
Anyway I hope this helps you and anyone else who may be having the same questions and / or concerns.
Happy Drawing !