Draw At Your Own Pace
Drawing has alot to do with seeing than it does sketching lines on paper. A good artist trains oneself to see well understanding the movement of ones subject. The more you draw, the quicker you will become at it as goes for anything else you train for in life. Drawing is no different. Everyone has their own pace according to how one thinks. I, myself am a slow drawer who begins a drawing and may put it away for awhile only to come back to it another day after I have a brand new perspective of how I want the drawing to be. Some artists are fast drawers in which they begin a drawing and finish it within a few hours maybe in the same day or the next. If I am given a commission then I have no choice but to begin and finish a drawing, but when drawing my own personal pieces I usually take my time to make my next one better than my last best one.
Whether you want to be the kind of artist who finishes a drawing at a quick pace or a slow pace it is really up to you. As long as you are satisfied with what you finished drawing looks like and make a constant effort in improving is all that matters.