Unless it was sent by express, parcels will be delivered between 8.00 and 17.00 monday through friday.
If you are at home at the time of delivery you will pay the postman.
If you are not at home he/she will leave a note in your mailbox with the details of the parcel. This gives you two options, either you take the note to the post office and pick up the parcel by yourself or you call the number on the note and ask for a second delivery.
Please note that if you were not at home at the time of delivery you will have to wait until the next day to pick it up at the post office.
In case you chose a second delivery and you call lets say on a monday, the earliest next possible delivery date will on the following wednesday.
More info can be found on
http://www.swisspost.ch/ (available in english)