The speed of light is NOT 343 m/s. That's the speed of sound.
You HEAR the explosion after
(5,400 ft) x (1 meter / 3.28 ft) x (1 sec / 343 meters) = 4.80 seconds.
The speed of light is 299,792,458 m/s.
You SEE the explosion after
(5,400 ft) x (1 meter / 3.28 ft) x (1 sec / 299,792,458 meters) =
0.0000055 second .