You can use Class function for this and use variable to input the days value for the days interval to show on the chart please see help from the QV help
Create variable x and and used it in place of the day dimension.
Creates a classification of expressions. The bin width is determined by the number set as interval. The result is shown as a<=x<b, where a and b are the upper and lower limits of the bin. The x can be replaced by an arbitrary string stated in label. 0 is normally the default starting point of the classification. This can be changed by adding an offset.
class( var,10 ) with var = 23 returns '20<=x<30'
class( var,5,'value' ) with var = 23 returns '20<= value <25'
class( var,10,'x',5 ) with var = 23 returns '15<=x<25'