It's like putting your car in a parking garage, no?

After dropping off the ladies at the dance the Bennets' carriage would simply go someplace else and "park" whether a nearby coaching inn or private stable or under a tree or behind a wall The coachmen would usually take the opportunity to socialize with the other coachmen from the other families at the dance. They wouldn't unharness the horses so yes, the carriage and horses would be kept waiting for when the family was ready to leave. If the weather was cold and there was an inn nearby the coachmen would usually get a stable boy to keep an eye on the horses and carriages and hang around the inn's bar till they were called for.

By the way, keeping the coachmen outside in the cold? Trust me most employers in those days weren't too concerned.