I have a sheet, with each row containing one record. Column A contains a
date, and column B contains a department. The contents of the column A
(date) are either a simple date "dd/mm/yyyy" format or a timestamp e.g.
"dd/mm/yyyy hh:mm:ss". Duplicates are allowed in Column A, Column B, Column
A + Column B.

I needed (ideally) a worksheet function that would allow me to obtain the
following information:

Based on a START DATE, END DATE and DEPT NAME return to me the number of
times I have the DEPT NAME occuring in my data for between the START DATE and
END DATE (both dates included) but counting multiple rows for the same date
as only 1 record. Thus if I have 27 rows for the same department with date
July 15, then it should give me only the value 1.

The time-part in the timestamp format can be ignored. It exists because of
input data coming from various sources and some sources store time and some
do not store time.

How could I do the above with a worksheet function?

Many thanks.