generate a series of dates in progress-db
Disclaimer: I'm not familiar with progress-db.
generate_series() is a PostgreSQL, set-returning function. AFAIK, generate_series() is not natively available in any other DBMS. (Except maybe in DBMS that are derived from PostgreSQL: Redshift, Greenplum, etc.)
You can get the same effect from most DBMS, though. There are a lot of ways to do that; I don't know whether progress-db supports any of these.

Program a stored procedure.
Use a calendar table.
Use a common table expression (CTE). (Not supported)
And I'm sure there are other ways.

A calendar table seems like the &quot;lowest common denominator&quot;. It works in all SQL DBMS. For whole days, 100 years takes less than 40k rows. A hundred years of whole minutes takes about 53 million rows. Your query, running against a calendar table of 100 years of minutes (53m rows, near worst case) boils down to this.
select distinct cal_minute::date as cal_date
from caltest
where cal_minute between '2021-01-07' and '2021-01-12'
order by cal_date;
----
cal_date
date
--
2021-01-07
2021-01-08
2021-01-09
2021-01-10
2021-01-11
2021-01-12

On my computer, which isn't anything special, it consistently runs in less than 10ms, and most of that time is sorting. If the order of rows doesn't matter--and it probably shouldn't--it runs in less than 3ms. (A wider range will take longer, of course.)
Against a 40k table of just dates, the equivalent of your query clocked in at about 0.1ms.