I'd suggest activating your passes 7 days before your departure from Japan.
I think you mean activate it before leaving Tokyo. If you are coming in late march or after March, you can take advantage of the new Suica-Nex combo (see other thread), so you can ride into Tokyo for 1500 yen on the NEX and have 2000yen on your Suica card to ride around until you activate your JR Pass for the rest of your trip into Kyoto and back to Tokyo and back to NRT.
your round trip Tokyo-Kyoto-Tokyo on the Hikari RailStar shinkansen,
The Hikari Railstar runs west of Osaka, for Tokyo-Kyoto-Tokyo regular "Hikari Shinkansen" trains run.