Time Stamp of Incident with maximum wait time.

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Hello,

I'm trying to retrieve the timestamp of an incident with maximum wait time. 

From the inc_performance table, I'm able to retrieve the maximum wait time using :-

if (inc_performance.intv_type=11, max(date_diff(inc_performance.time_end,inc_performance.time_start)))

However, if I extend the same logic to print the time stamp :- 

if(inc_performance.intv_type=11 &
date_diff(inc_performance.time_end, inc_performance.time_start) = (max(date_diff(inc_performance.time_end, inc_performance.time_start))), inc_performance.time_start)

I'm getting a "No Value" output.

Is there a way to retrieve the Incident information?