Define sort order at same time as creating a conditional columns

I am using a conditonal column to group durations (days) into custom groups "Range"
eg less that 30 = less than 1 month
else if less that 60 = 1 to 2 months
else if less than 90 = 2 to 3 months
otherwise = great than 3 months

As my "Range" custom column is not text it does not sort in this order (instead alphabetically)- and cant sort the column by duration as that is not unique. So I know have to do another conditional column to specify sort order.

Would be great if while constructing the first conditional column you could tick a flag to say - sort by this order. Or have an extra cell on each line so you could specify a sort order number as you go.