Exact-date postal service

I will be leaving Japan 3 weeks before my friend's birthday and I was wondering if it's possible to leave a gift for her in a local post office (in Tokyo) with exact "delayed" delivery date specified on it? It would really save me much troubles and even more money since international postal services in my country are insanely expensive.
If there is such a service, does it have any name? I can speak Japanese so I think I'd manage to explain what I need in a post office but the name would help a lot.

Thank you!

Den,

I'm not sure whether the Post Office would be able to do something like that, but there is no harm in asking at the counter. I would also suggest contacting one of the takuhaibin companies (Yamato, Sagawa, etc.) to see if they can deliver something 3 weeks later, as their delivery services normally allow you to specify the delivery date and time.

Thanks for the Takuhaibin idea, I've completely forgot about them!