No one can answer exactly that how long it will take to get backlink. But once Google crawls that particular page of the blog on which you have commented then after there is a chance to get backlink from that particular blog.
Technically, the second that link appears you have a back link even if Google doesn't crawl that page. That said, once Google does crawl that page it will only benefit you if the link is a "do follow". If its a "no follow" link, like many are than you might be waiting for nothing.
Yes i totally agree with the "scholarsjunction" in majority blogs when we post comment on it it held on moderation and even many blog admins not approve your post even after the six month or year. So it's will be good if you will use the auto approve blog list that will give you backlinks at the same time of post comment on it.
If Blog admin will approve your comment and after that Google boat crawls that particular page with your comment then there may be chance to get backlink, but it is not necessary some time after crawling we may not get backlink. So you can say that it will not be said exactly that how long it will take to get backlink as JasonWright337 said.
it can not said that hoe much time taken .it the matter of on which blog you write your comment and it should be a high rank good quality content blog
Totally depends on the moderator. If the moderator is not lazy, you can get back links with in few hours of posting.
Some blogs are auto approved our comment publish there at the same time of post comment but some blogs are not auto approve in which first website admin check our comment and then approve it. In some cases website admin not approve our comment.
Yes, but to show your link profile natural, you don't have to think of nofollow or dofollow, just keep building links whatever quality and relevant sites you get.
Find do follow blogs using special searches such as "subject:.edu -captcha -nofollow “leave a comment”
It Totally depend on Google or other search engine, when they will crawled the blog your comments will also get crawled and backlink will be attached to your website. No one can tell you the perfect answer.
Blog commenting good strategy SEO off page, if you comment your theme wise then get more traffic as soon as....
No one will give you exact time duration of getting backlink but once crawler crawl that page, you will get backlink from that blog and it also depend on follow or no follow tag. If it is no follow then your link will not get any linkjuicce from that blog...