...procedures to be followed? Please explain the no. of exams to be written and the corresponding eligibility? Also detail about the basic requirements needed? What is the maximum duration to become an underwriter?

There isn't a "maximum duration" but if you have no experience, unless you want to try being a wholesaler, you have very little change of getting hired in.

You're talking two different horses here - I don't know of anyone who "underwrites" both general and life lines. Companies usually either sell one, or the other. When they DO sell both, the lines are strictly divided. I don't know of ANYONE who underwrites both.

Requirements vary by state. But getting the appropriate license is easy; getting a JOB in underwriting can be very, very hard. Getting free training from a company, means you have to have the job offer first.

Usually the job comes first, then the training, etc.

Unless you're a wholesaler, you don't NEED a license, btw.