what is the average time taken for friendship to be established?

I think it takes time to build a lasting friendship, it takes time to personally know a person, and to gain somebody's trust but I do agree that you can gain a friend within seconds, if you have the same interest, but they're just mere acquiantances I think, you can't depend on them that much.

Friendship takes time to build. When you meet a new acquaintance, you have to assess if the person is to your liking, say, if you have a common denominator that you would like to pursue. If you don't share the same interests, you can't be friends. If you like the same things, you can grow with each other by spending time talking of doing things together. And the friendship grows... Friendship does happen overnight. It is built with firm foundation.

I think one can meet someone and begin a friendship immediately. But true friendships are made through shared experiences and that often takes time. I have good friends that I continue to share time with for over 40 years. Since childhood. You are right that we should open up even if we don't know someone if we are to become friends.

Having an "average friend" take XXX of your time. Nobody knows when and how fast you ca establish friendship with people. It depends on the personality of both parties. ^^

Tough question ... You can become friends with someone after 5 minutes of talking to the guy/girl but it might also take months or even years to establish a TRUE friendship ...