Similar to negative dates in Excel, Excel will display unending hash symbols for negative dates inside an Excel Cell. Note that I am using default 1900 date system in my Excel Workbook. Click the following link to learn how to change Excel date systems.
To check how Excel handles negative time values, let us enter a negative decimal number in an Excel Cell, which is formatted as number. In this case, I am entering -0.04166667 as the time decimal number. The decimal number 0.04166667 represents one hour in Excel. Again, note that currently the Cell is formatted as number. Refer below image.
Right-click the Cell and select "Format Cells" from the context menu.
Format the Cell as Time, as shown below.
You can see that the Excel fills the entire width of the Cell with hash symbols, if you have negative time. If you try to increase the width of the Column, Excel will fill the entire width again with hash symbols. Refer the image shown below.