I live in the country, about 150 miles from the DFW area, and have a pretty open sky with which to observe high-altitude flights, which out here are pretty isolated.
I’ve noticed now with very clear consistency that there is a 7-minute lag between when the flight passes and when FlightAware shows it being there. It’s even more delayed with Flight Explorer AVWeb Edition, which lags by 11 minutes!
I know this is not Flight Explorer (and I’ll put the question to them too), but I remember when I was using them 3 years ago there was no lag at all. I would see a FedEx DC-10 on the map, look up with binoculars, and there it was! Now I’m having to wait for the radar returns to paint the plane over my house with both systems.