Ok I got the file by email and returned with the following

Well, that took a little creativity, but I think I have a solution.

First, let's look at the problem. If you go to your source data cell C92 which shows a value of 00:11:26 and in formatting change this to the number and increase the decimals. You will see that the actual decimal number that represents this time is 0.007940. This is the actual value that your chart is displaying. If you change the number format on the label of the chart and increase the decimal, then you will see these are the same.

Unfortunately, both dates and times are just numbers to Excel and Excel is doing exactly what you tell it to do.

I am assuming you want to plot 11 min, so we need to covert 0.007940 to 11 somehow.

When we have a duration in minutes, if we multiply the duration by 60 ( as there are 60 min in an hour) and then multiple again by 24 (as there are 24 hours in a day) we can convert the .007940 to 11.43. 26 second is 43% of a min, hence the decimal.

So I first changed the custom formatting you had set for duration type on the prep sheet from mm:ss to number. then I updated the prep sheet formula so that if Duration is selected then carry out the above calculation, otherwise leave the calculation as you had it.

It might not be the fix you need. Fingers crossed it is, please do check the file and let me know