If you change the base date to 1904, then you'll see negative times.

Tools|options|calculation tab|check the 1904 date system.

But this'll change existing dates to about 4 years into the future.

You can adjust/fix the dates by putting 1462 in an empty cell.
Edit|copy it.
Select the cells with the "bad" dates.
Edit|Paste special|click subtract

John Sheakley wrote:

Negative dates or times are displayed as ####. The cell retains the
negative value. How can I display negative time as "h:mm AM/PM" in red or
with a negative sign? The cell should retain the negative value.

--

Dave Peterson