The OP's solution seems to solve this problem though - if it's the last hour of 'work time' then people can stay for at least that hour and then if they have to

The OP's solution seems to solve this problem though - if it's the last hour of 'work time' then people can stay for at least that hour and then if they have to leave at the normal time, they can. If the socialisation time is always outside work hours, then yeah, people with young kids will basically never come.