It doesn't take long for the thrust to disappear. The engine "fire" goes out almost immediately. As a ground maintenance engineer, I used to put safety cones a meter or so in front of engines shortly after engine shutdown (sometimes, I'd say, as quickly as 30 seconds). The noise of the engine blades spooling down was a little intimidating though.
I'd leave the cones at the back of the engine a little longer, but that's only because I didn't like burnt fuel fumes
Sometimes cargo (un) loaders would approach the aircraft before the engineer at the nosewheel gave the thumbs up, but they didn't seem to suffer any ill-effects.
Perhaps the pilots can comment on what %rpm they turn off the red beacon/strobe light?