I'm new to the forum and really hope you guys can help me out.

My spreadsheet has 9 columns. Col A has the date and time (eg 4/12/06 4:00
AM). The last column (J) is the difference between the consecutive cells with
the dates. For eg. Cell A2 is 4/12/06 4:00 AM ; A3 is 4/12/06 7:45 AM.
J3 calculates the difference as 3.75 hrs (A3-A2). This continues for 90
rows down.

I would like a formula or method where I could select a date range or a
particular period (start and end OR min and max) within the 90 rows and sum
the respective values for the same period in the last column.