How do you set the clock on a 2000 Suzuki grand Vitara?

This link covers several possible methods, depending on which stereo you have.
http://www.suzuki-forums.com/1g-1999-2005-vitara-grand-vitara/29577-how-set-clock-standard-radio-vitara.html

I have a 2001 "normal-not-Grand" Vitara with a stereo with a single CD player. What worked for me was pressing and holding the up arrow (bottom right corner of stereo unit) to change minutes, down arrow for the hour.

The link above implies that whatever stereo came with your Suzuki, it is probably a Clarion, so perhaps their website/customer support might be of assistance if the methods they suggest don't work.