This applies to Flexi Passes. With a Flexi Pass, you have a certain number of days WITHIN a certain period, either 1 or 2 months. Your 1- or 2-month period begins when you activate your pass. You can make as many train journeys as you like in one day, as the passes are restricted by days not journeys.
For example, if you start using a 4 day pass on the 23 March you then have 3 remaining other days that you can use your pass until the 22 April inclusive.
You may use your pass as many times as you like within a day.