I have a cell into which I would like to input a time value, either negative or positive from which other cells will perform calculations.

When I enter the time as a positive value it works fine, however if I attempt to put the value in as a negative, i get a popup that says "The formula you typed contains an error. If you are not trying to enter a formula avoid using the - sign."

If I format the cell as -h:mm, it has no problem processing the value entered, however I cannot enter a positive value. This same error occurs no matter how the cell is format, from General, to Number, to Time, to Custom Time.

I have the 1904 date system enabled if that helps with the problem solving.