OK, I see the file.
On the tab "Average Days to Resolve", I see a chart with columns and a line. The line series is defined to take its values from a range name "AvgDifference". That range name points to ='Group Report'!$D$2:$D$12 and the values in that range are NOT TIME VALUES. They seem to be the total number of resolved tickets. These are the Y values plotted on the secondary Y axis: numbers that range from around 5000 to around 13000. The Y axis is set to a major unit of 0.0208333.
Next to that data called "AvgDifference" is another column with data labeled "Avg Time to resolve", but these are not time values either.
Can you please explain what you would like the chart to show? What should the red line show? If you think these need to be time values, are we talking about elapsed time (like, it took 48 hrs to resolve the ticket) or are we talking about a time of the day, like something happened at 3:30 PM
Where should these time values come from? You say above that "the column that I am using for the time value is already in the hh:mm format ". What column is that? Your data does not point to it.
By the way, it is not good practice to hide data by formatting it white on white. Looking at data ranges and range names, they appear to be pointing at empty cells and can cause quite some confusion (i.e. wasted time) when trying to troubleshoot something.