On average and ideally I can draw a page in a day. So for a monthly comic that is comprised of 20 pages, it takes me a little over three weeks to complete including the layouts and the cover. However, deadlines and schedules play an important part on my output resulting in variations on how many pages I can do in a day. Sometimes due to various reasons my deadline can be pulled back or a script may come in late so I have to do more. There has been days when I had to draw three pages in one day.
For covers, it takes me two three days on average. The actual drawing usually takes one day but the preparation and approval stage can take a few days.