EH-Net

If I register for OSCP . I will get access from where I can download the Video Training which are of 7 hours and along with that I will receive a 30 day online LAB . I want to ask will my LAB duration start when I will purchase the product or will I study the Videos , make notes and then after that I will request for the lab access which will offer me 30 days to practice .

You'll receive your personalised notes and vids at the same time as your lab access starts. (You book for everything to start on a certain day)

Doing things in the labs goes hand in hand with the vids as the videos are instructional in nature. Everyone has there own learning style, the way I did (and am doing) it is to read the notes through once just to get an idea of what the course entails, then do the labs along with the videos (heavy use of the pause and rewind buttons). I'm not saying you'll get nothing from watching the vids without doing in the labs, but doing them together certainly helped (and is helping!) me grasp certain points.

--edit--
Just noticed the subject of this thread mentions the exam. You've got plenty of time between the labs ending and when you need to do the exam. IIRC you can book the exam to take place up to 90 after your lab time ends.