While studying BSc the student is eligible to appear for the Paper SB during the first year of the BSc only. So if you don't appear for the KVPY examination in your 1st year of BSc then even if you qualify the SB examination, then also you will be not awarded the scholarship amount. So giving the examination will be of no use for your career.

For more information regarding the KVPY you can consider the link below:

http://www.kvpy.iisc.ernet.in/main/index.htm

I hope this helps. Wish you a great eve!