Formatting time as hours and minutes above 24 and no date.

I am a basic user of IgorPro using the dialogue boxes pretty much exclusively. I am trying to produce a simple scatter plot. The Y axis merely has 5 values representing risk levels. The X axis has time data measured in hours and minutes. The times may be negative numbers as an event may have begun prior to the reference time. I cannot seem to format the X-axis to display just hours and minutes with values beyond 24 - e.g. 44:30. Also I do not require a date. I have attached a screenshot of a test plot. Clearly there is something about time handling I am not understanding.
Any advice would be appreciated. Axes dailog box.jpg (88.39 KB) Test_Scatter_Plot.jpg (35.7 KB)