Custom Slicer for Future Time Periods

Anonymous , I think you should try measure like this example

//used date table

Measure =
var _max = maxx(allselected('Date'), Date[Date])
var _min = eomonth(_max,-3)+1
var _sel = 'Time Period'[Time Period Slicer])
return
Switch(True() ,
_sel = ="Next 2 Months",calculate(Sum(Table[total hours]), filter('Date', 'Date'[Date] >= Min && ' Date'[Date] <= _max)),
_sel = ="All Months",calculate(Sum(Table[total hours]))
)

or

Measure =
var _max = maxx(allselected('Date'), Date[Date])
var _min = eomonth(_max,-3)+1
var _sel = 'Time Period'[Time Period Slicer])
return
Switch(True() ,
_sel = ="Next 2 Months",calculate(Sum(Table[total hours]), filter(all('Date'), 'Date'[Date] >= Min && ' Date'[Date] <= _max)),
_sel = ="All Months",calculate(Sum(Table[total hours]),all('Date'))
)

if needed refer

Need of an Independent Date Table:https://www.youtube.com/watch?v=44fGGmg9fHI