Hello Pauwheewoi80
There is actually no minimum rental term yet a standard rental term.
Did you notice that there is an English website as well?
https://sbb-tickets.cc/en/travel-information/stations/services-station/lockers/lockers.html
There is stated:
From 6 hours: additional payment required on collection. The locker will remain closed until the payment is made.
In order to know the cost, you have to choose a station first as the locker prices vary from the station to station. Simply enter the station name into the input field where it reads: Find station.
Kind regards,
Roland