Although a US regulation, the following bit from the US operating rules (also known as CFR 14 Part 91) might be interesting. These cover all flights (airlines and general aviation).
91.105 - Flight crewmembers at stations.
(a) During takeoff and landing, and while en route, each required flight crewmember shall (1) Be at the crewmember station unless the absence is necessary to perform duties in connection with the operation of the aircraft or in connection with physiological needs; and (2) Keep the safety belt fastened while at the crewmember station.
So, alas, other than a quick hello while on the way to the rest room, no socializing is permitted. Just one more example showing that we are no longer in the "golden age" of air travel when such visits were considered part of the Captain's duties.