I have a button in an app that allows a user to enter a fixed period, i.e. they specify the start and end date and it always stays the same. I have another button that allows them to enter an offset/delay and a length/duration of time that "stays current" but I can't think of a single word that would fit on my button that would describe this.
For example, let's say I select this "stays recent" button and specify a delay of 3 months and a duration of 12 months, that means if I were to look at the data in June 2014, it would show data from March 2013 to March 2014 (12 months, from 3 months back). Then if I were to go and look at the data in October 2014, it would show data from July 2013 to July 2014.