JR pass

Hi,

I am travelling to Japan from UK at the end of the month and want to get a 7 day pass. From what I understand I have to activate / exchange my pass on arrival? I am going to Niseko for a week at the start of the trip so want the pass to begin a week later. Do I have to exchange as soon as I arrive at Tokyo airport or can I do that at a train station the first day of rail travel. I am wanting to do the shinkansen from Hokkaido to Tokyo so also want to check that is covered by the pass.

Thanks

Phil