90th Percentile Issues (Not displaying correctly)

CPage-WF 

Yes.  If you do not already have an Index, you can create a Calculated Column as follows.

NOTE: I am assuming you have an ID in your table.  Since you have duplicate values in the Unit Turnout Time, you need a way to differentiate between duplicates to assign different ranks for the same Unit Turnout Time.  In this example, I'm simply adding the ID to the Unit Turnout Time to get a unique value on which to properly rank all values.

Once your Index column exists, just update the measure to refer to it inside the CALCULATE.

Hope this makes sense.

Nathan