Today Saturday 10th January 2015 is the last day for handing in your "second Christmas" goods at the post office.
On Saturdays, many local post offices are open, if at all, only in the morning. However, in larger centres or at airports, some are open much later.
To see opening hours, go to https://standorte.post.ch/
and click on "Öffnungszeiten" (= "opening hours").
The top clickable line reads "Poststellen geöffnet bis 20h" (= post offices open until 20h). That leads to a map of Switzerland.