I use an Excel 2000 spreadsheet to log sub-contract work hours - and
as the hours are then used to calculate charges I use separate hours
and minutes columns (start hh, start mm; finish hh, finish mm). That
seemed the easiest way to me.

Everything is working just how I want it, but....I now need to
introduce a night charge:

A shift can start anytime day/night and finish anytime day/night. If,
the shift includes ANY time worked between 1 am and 4 am I then need to
(a) invoke an extra charge and (b) do some other checks in a different
spreadsheet.

How do I get Excel to test for this? Thanks for your help.