There is a 0.0% chance that this happens (in my opinion as a paramedic). If I had to guess, 0.1% is probably the rough order of magnitude of the frequency with which doctors look at the PCR at all. We give a verbal report which covers the important details. I would be hard-pressed to come up with an error that could possibly waste an hour of someone's time.
"Did that quarter-second lag kill anyone? Was there someone who wouldn’t have died if the ePCR was just a little bit faster, fast enough to be usable? ... It could have saved the person the EMTs couldn’t get to because they lose an hour a week from extra PCR overhead."
Similarly, no. There is no situation in EMS where 250ms is the difference between life and death. It's not like the tones drop for a call and we say 'gee, I wish I could go help that person, but I still have this chart to write...'.
Performance absolutely matters (ironically, I'm a software developer for an EMR at my day job), but a little lag in an ePCR isn't going to kill anyone.