When and where to validate JR pass

Hi,
You can activate it at any time. And your first day does not have to be the day you activate it.
Please remember also that the day you activate it for counts as Day One - which starts and ends at midnight. So if you activate it and use it at 6 PM, your first "day" is just 6 hours long. Many people activate it just before they start riding their first train, which is fine. But you can't activate it in just any JR office or station - only the major ones listed here. So if you wanted to start using your pass from some small town, for example, you could activate it with a future date listed as the first day. Once it is set, it cannot be changed, so it is not a good idea if all your plans are still up in the air.

Regarding your use of the pass, you give no info on your itinerary, so it is unclear if even buying a pass is suitable for you or not. The cost of regular rail fare should exceed the cost of the pass during the same time period.

You can see regular fares and schedules on Hyperdia.

Best of luck.

We are going from Hiroshima to Kobe , then kyoto and the to tokyo. Looks like we are breaking even. As we can use it a bit in tokyo as well. Thanks for your help, Dave and Vishy

No trouble - enjoy your trip. You could always increase your savings with some day trips. Since you are going to be in the Hiroshima area, there are many places you could try if you have time.
Okayama is not far and it is famous for its castle, plus Korakuen, one of Japan's Top 3, and also the Handayama Garden. If you'd like to get off the beaten trail for a while, the half day hike up to Konpirasan in Kotohira is stunning. Going to Takamatsu is also nice - it has one of Japan's finest gardens also, called Ritsurin.
Hiroshima also has a number of good places. Miyajima is the most famous, and aside from Hiroshima itself, Onomichi with its temple tour and Kosanji Temple is spectacular. Just beyond Miyajima also lies Iwakuni with its historical bridge and castle on top of the mountain. And deeper into Yamaguchi there is the Akiyoshido which is a 300 million year old limestone cave 1km deep with an underground river and giant caverns.

Besides all that, north of Tokyo there is also Nikko, which is a great day trip.

You should be able to see a large variety of interesting places.

Best of luck.