No, tested evacuation time is not a realistic value, but it can show the Relative ease or difficulty required to get the folks out. If an able bodied test passenger can egress in 90 seconds, it is a fairly reasonable assumption that someone who moves half as fast outside an aircraft would take about 3 minutes to complete the same egress.
As for the folks that use a straight back/isle chair, they, like lap kids, are pretty much out of luck. If a crew member decided to block the isle for 15 minutes assisting a handicapped person while trapping a bunch of able-ish bodied pax, to me that would be something like malpractice or neglegence.
But ...
It doesn't matter if everyone were a 20ish track star or not. At least 10% of the people will be on the phone, packing up a laptop while blocking the isle and getting annoyed with all the other folks who just want to get to a safe place.