Is the period between the entry of the second female employee and the entry of the third male employee considered an unlawful private seclusion (khalwa) if the male employee was the first to enter the software company where he works, which has between fifty and sixty employees and no security guard?

The scholars have mentioned the prohibition of two non-mahram individuals being alone together in a place where their sight and sound are hidden from people, provided there is no fear of a third person entering upon them. The definition of seclusion (khalwa) is a gathering where suspicion is not usually safe. It is better to leave when a woman enters upon you and wait until another person comes; because Satan may lead those in seclusion to forbidden acts. And it is not a condition for the prohibition of seclusion that the major indecency (fahisha) can occur. You must lower your gaze and avoid speaking with non-mahram women except within the limits of what is customary.