I laid down another temporary cable from Xend to 1Y2 (LSC rack) for also measuring the Q output of the DFD box. Then to get a quick measurement of these long cable delays, we used Moku:GO in oscillator mode, sent 100 ns pulses at a 100 kHz rate from one end, and measured the difference between reflected pulses to get an estimate of time delay. The other end of long cables was shorted and left open for 2 sets of measurements.
I-Mon Cable delay: (955+/- 6) ns / 2 = 477 +/- 3 ns
Q-Mon Cable delay: (535 +/- 6) ns / 2 = 267 +/- 3 ns
Note: We were underestimating the delay in I-Mon cable by about a factor of 2.
I also took the opportunity to take a delay time measurement of DFD delayline. Since both ends of cable were present locally, it made more sense to simply take a transfer function to get a clean delay measurement. This measurement resulted with value of 197.7 +/- 0.1 ns. See attached plot. Data and analysis here.