A minimum of 20.

If time permits, 25-50.

It varies from 30 minutes to more thru out the day. 10 is usually about it. Followers first then recents where I might find someone else I want to follow!

It really varies from day-to-day.  There are days I leave no comments (due to lack of time) but bookmark certain posts in part with the intention of commenting on them at a later date.  There are days I only leave 1-3 comments and there are days I leave 10 to 20 comments.  Just depends on how busy my day/week is.  The amount of time depends on the number of comments and how long my comment(s) are.  I try never to do the "thanks for sharing" kinds of comments that I see a few people leave just to reach the max number of comments per day  to maximize points earned.  Earned... ha!... that's good one.

Bob, it usually leave about 22 comments and it probably takes me about 90 minutes to two hours as I do read the entire post.  My comments are spread out  many times over the course of the entire day.

I do about 25 comments per day. I answer 10-12 questions per day. It takes about an hour with the reading of the posts.

I average 10 blogs per week, and 20 comments per day, minimum.

Around 30 minutes of comments and on some days I do spend more and do some catching up.

I don't return comments and give them out based upon time. Although it can take a lot of time. I try to return those comments left on my posts. I also have regular followers I read and they read me. I consider that polite to comment on them. I leave at least 20 comments a day. 

Bob, there are days I can barely get 10 done, and some days I leave 30.   Just depends on time available.

As many as i can, i check my favorites first and then as time allows expand out leaving a comment on every blog i read to let them know i was there

I used to do 20 or so, but now I'm so busy, it's prob more like 10 and some days less.  I'm trying to reduce time spent on here and reallocating.

At least 20, try to keep it brief as time is limited.