How long exactly is a month pass valid?
July has 31 days, so the pass is also valid for 31 days. February has 28 days and a pass is therefore valid for 28 days.
Here are some examples:
First travel day 1 July: pass is valid from 1 July up to and including 31 July.
First travel day 12 July: pass is valid from 12 July up to and including 11 August.
First travel day 1 February: pass is valid from 1 February up to and including 28 February (or 29 February in a leap year).
First travel day is 15 February: pass is valid from 15 February, up to and including 14 March.