Compare output of logic gates but ignore their difference due to propagation delays
You only want to give a warning if the input trigger is longer that the output trigger, so...
Use the trailing edge of the output trigger to clock a 'D' F/F whose Data input is connected to the input trigger, and take your warning from the F/F's Q output. Waveforms look like this:-

Top 2 traces shows input trigger shorter than output trigger. High to Low Clock occurs when when D is low (circled), so the F/F Q output stays (or goes) low.
Bottom traces show what happens when the input pulse is longer than the output pulse. F/F's Q output (red) goes high when the high D level (circled) is clocked into it.
The 'alarm' output output will remain high until the next pulse, when it will either stay high or go low again depending on the relative pulse widths. This may be good enough for your purposes. If not then use that output to set a latch or clock another F/F which must be manually reset by the user.