Five feet from the front wall

For the best playback clarity, it’s advisable to position your speakers at least 3 feet away from the nearest wall, measured from the tweeters. This spacing minimizes sound reflections, which can otherwise be perceived as part of the direct sound and adversely impact listening experience. Human hearing tends to distinguish reflected sounds less than 5 milliseconds apart as part of the direct sound. With the speed of sound measured at approximately 1100 feet per second at sea level, the minimum spacing required for reflected sound to be longer than 5 milliseconds is calculated as (1100 x 0.005) / 2, resulting in 2.8 feet, which is rounded up to 3 feet.

That is the wrong way to look at it lanx. Sounds that reach your ear after 10 ms are perceived as an echo. Less than 10 ms and they are perceived as one with the direct sound. 

I'm not sure where you received that information from. The reference to a 5 ms time interval was made by Haas (1951), who stated that a single reflection arriving within 5 to 35 ms can be up to 10 dB louder than the direct sound without being perceived as a secondary auditory event (echo). The shortest possible interval is 5 ms.  You can find this information in the following reference.  Should you need more details, let me know.

Haas, Helmut, The influence of a single echo on the audibility of speech, J. Audio Eng. Soc., Vol. 20, Issue 2, pp. 146-159, March 1972 (English translation by Dr. Ingr. K.P.R. Ehrenberg of Haas’ original German paper published in Acustica 1, pp. 49-58, 1951).