7 day ticket - When exactly does ir expire?

Hello,

I'll be in Japan in october.
I'm planning to leave tokyo towards Kyoto on oct 14th and come back on the 21st.
Consering that the ticket is valid for 7 days, would I be able to get a 7 day ticket and go back to tokyo on the 21st without having to get a 14 day ticket?
If we consider 7 complete days, the ticket should expire on the 21st by the time I validate it on the 14th.

Would that work?

Thanks