Then the ability to calculate dates in a script (based on the calendar of the computer on which scheduler is run) would be of benefit.
My reports take a yyyy-mm-dd prompt
so a line
prompt = Format(Cstr(CVar(Date)))
gives a prompt that is the computer's current date.
You can use basic arithmetic with the dates and there are functions such as Day, Month & Year to assist.
Day(Date) gives the day count to current date.
If deducted from the Date within the Cvar function, then you have the last day of the previous month.
Removing the date field and adding -01 can give the first day of the prior month.
i.e.
strendd = Format(Cstr(Cvar(Date-Day(Date))),"yyyy-mm-dd"

strstartd = Format(strendd,"yyyy-mm"

+ "-01"
prompt = strstartd + "|"+strendd
If you're doing quarterly, then adjust to:
strdate = Cvar(Date-Day(Date)-89) 'go to last month & then 3 months prior
strstartd = Format(strdate,"yyyy-mm"

+"-01"
strendd = Format(Cvar(Date-Day(Date)),"yyyy-mm-dd"

prompt = strstartd + "|"+strendd
Obviously, this is pretty basic and doesn't adapt for working days, public holidays, but at least keeps things automated.
HTH
lex