This option allows to have any release time between 100 ms and 1 second on position 3, without altering any of the other positions from the original 670 design/control circuitry, so positions 1, 2, 4, 5, 6 all remain unchanged.
I also recommend changing position 4, from the 5 second release time to 2 seconds, if you prefer using more "modern" release times. Please let me know, I don't charge any extra for that.
Here are the original Time Constants from the 670 :
IMPORTANT :
Please note that the filters on the Side-Chain allow less compression at low frequencies, thus allowing no distortion at low frequencies on very fast release settings.