I do remember an Irish singing session in the 1970s, where the landlord told us we'd have to leave soon, because the police, who would be patrolling certain local sites for bombs etc, would be in for their drink shortly.

However, there is something to be said for a fixed closing time. When I went to a session in Scotland, people just dropped out and departed one by one until late. But when there's an 11pm closing time, as in England, we generally try to finish on a tune that we all know and enjoy playing. Then we have a general milling-around time while we take our farewells (my Scots mother used to call this "bonnet crack" - the crack you have while you're putting on your flat cap to go home). It's the time when you arrange future contacts with each other, share scraps of gossip, pass on any tune names or e-mail contacts, remind each other when the next session is, and so on, and it's an important social part of the evening. Without a fixed closing time, this just doesn't happen. And the open-ended session may not actually work out any longer, it may just be later in both starting and finishing.

Marje