Off-peak tickets incl. the upgrade for Express bus are valid for 1 person and 3 children (aged 6–14) Mon–Fri from 9 am–4 pm and again from 6 pm to 6 am the following morning. On Sat, Sun + public holidays they can be used all-day. They are available as a monthly season ticket or even cheaper as an all-year season ticket.
With the monthly off-peak season tickets, you can choose the first day it is to be valid yourself, e.g. from the 8th of a month till the 7th of the following month.