I have a spreadsheet that contains all the parts that me manufacture and the
process times for each operation to make these parts. The process times are
in minutes per piece.

What I am wanting to do is calulate the start day for each operation by
deducting the process times from an end date (excluding non working days, we
currently work 24hs 5 days per week).

For example if we are making 100 of part no. 123ABC it would caculate as
follows:
Process times:
Operation 1 = 5 mins
Operation 2 = 10 mins
Operation 3 = 15 mins
Operation 4 = 60mins
End date = 31/10/06

Op 4 ~ 31/10/06 - (60mins x 100 = 4d 04h 00mins) = start date 24/10/06
Op 3 ~ 24/10/06 - (15mins x 100 = 1d 01h 00mins) = start date 20/10/06
Op 2 ~ 20/10/06 - (10mins x 100 = 0d 16h 40mins) = start date 19/10/06
Op 4 ~ 19/10/06 - (05mins x 100 = 0d 08h 20mins) = start date 18/10/06

I currently have a spreadsheet set up that calculates starts dates for a
differnt department but the process time are in days so it is quite easy.

If this is difficult to express in words I can forward my email address so
the you can send me an example that I can manipulate.

Thanks.