Delayed Activation of the JR Pass

Hi Guys

I land in Japan on a Saturday evening, and fly out the following Saturday (8 days). Can I activate the JR Pass when I land at the airport, but have the usage start from the Sunday, that way I can use it from Sunday to Saturday....or if I activate it on the Saturday, does that mean I'll only have to Friday to use it?

I don't really want to figure out where to activate it when I'm in Tokyo, I imagine it'll be a lot easier to do it at the airport.

Thanks!