It also has the potential to cause confusion, since 1/24 and -1/24 are
both displayed as 1:00:00 AM (i.e. there is no formatted indication that
the time is negative).

Jerry

Tom Ogilvy wrote:

If you use the 1904 date system in excel, you can use negative time
(tools=options=calculate tab).

However, this will probably make all your dates off by 4 years.

If you want to use decimal number of hours you can

=(a1-a2)*24