On this link about the 620 Squadron, scroll down to: 21st September, 1944
https://www.pegasusarchive.org/arnhem/war_620sqn.htm
They say 11 Stirlings were dispatched on that day. Two failed to return and two others landed at other airfields, one at Manston with a wounded rear gunner and the other at Woodbridge with a wounded Air Bomber. No mention of Biggin Hill. (Unfortunately, they don't identify the two planes.) Looking at the flight times it appears that LJ580 and LJ892 had the shortest flight times that day, 3 hours 50 minutes each. Those may be the two planes that landed "early" and at the airfields closest to the coast.
UPDATE:
I found that LJ580, flown by Fg Off Deacon landed LJ580 "X" at Manston in Kent in foggy conditions. His gunner, Fg Off Smith had a bullet wound through one of his lungs and was admitted to Manston Station Sick Quarters in critical condition.
The above info is from the book "Stirlings in Action With the Airborne Forces: Air Support to Special Forces and the SAS During WW11", by Dr. Dennis J Williams, Page 169 (according to Google).
Search for Deacon on the Google books link:
https://www.google.com/books/edition...sec=frontcover