You cannot directly set a custom time-frame as a filter on the Purepath page. For your case, What you will have to do is from the Service details page, set your analysis range to 2 hours (you will need the global time-frame to be at least a 6 hour window to analyze 2 hours). and then set the analysis range on the chart to the 2 hour time-frame for 2pm-4pm. then select View Purepaths from that screen. See screenshot for reference.