I get up early and do an hour or so writing a blog or two. Then I spend an hour or 2 "marketing". I think you need to spend at least 2 hours a day to make it successful, but I could probably spend a bit less time writing.
It also depends on how many blogs you have, and whether you're interested in the subject or not. If I know a subject it takes me no time to actually write the posts. Also, the more you write the quicker it will get. It depends on whether it's a full time income for you or not.
About 4 hours a day at the moment. Im off work for a short while. It will be a lot less when Iam back working.
I spend around 5 hours. Thats too long, but my blog is just one month old, and I just want to make sure that I build backlinks for my blog to impress Google in their next PR update. Also, first few months is very critical stage for any blog so I am left with no choices but to work hard on getting traffics.