I wrote a really ranty post and left it in draft because I couldn't quite find the right tone; and then I discussed it with Carole the Photographer, who knows a lot more about two relevant subjects than I do - dance-as-performance, and Argentine culture. It turns out there might be a really nasty cross-cultural "gotcha" here. Which is more interesting than rants. [Edit: she was really talking about stage shows ,not shows in milongas, see comments, but I actually think it's relevant because the kind of performance I'm talking about acts like a stage show and forgets that it's in a milonga.]
So here to begin with is my very British rant - which probably a lot of Europe would agree with - and which represents how I actually feel about this. Please don't be too upset.
If the milonga is only three and a half hours long,
And you are giving a performance,
And most of the people are there to dance socially (or even if some of them aren't),
And even if your performance is quite exceptional (or especially if it is, to take a wholly imaginary example based on many experiences, totally phoned-in 'salon' stuffed full of silly-ass back-sacadas)
And no matter what your mates in the crowd do (buying your own hype is a bad bargain even for princes),
Here are some things you do:
You move briskly from dressing room to stage and back,
You refrain from excessive faffing between tracks,
And you sit down after a maximum of four.
Sitting down after three tracks or less might get you a reputation for modesty, professionalism and good manners.
Going on longer doesn't convince people you are stars. If you are, they'll be able to tell, by watching your dancing. Also, you sound ridiculous preaching about social dancing if you make it it abundantly clear that you don't give a monkey's about other people's.
I know it's a tough job, but sitting down is not the toughest part.
Here's the problem, as Carole explained it to me: In Argentina they expect you to go on as long as you are allowed, and they signal you when to stop. They also basically assume that if you want to go on longer about something - anything - it means you are passionate and sincere about it. And if you are brief, then you aren't.
In Britain they won't tell you to stop; they expect you to know, accurately, when to stop, taking into account both your own popularity and other people's time for social dancing. They expect that as part of your professional skill. So, Carole tells me, travelling Flamenco shows and such-like always shorten their acts for the second performance in London, and some of the more intelligent ones work on imaginative curtain calls to replace planned encores and manage the process of getting off stage to everyone's satisfaction.
And - here is the really nasty bit - if you go on and on about something, the British think that you are insecure and don't really believe what you are saying.
"The lady protests too much, methinks"
Anyway. Three is safe and communicates modesty and a genuine interest in social dancing. Four may be demanded if you are genuinely popular, in which case it's polite not to waste time. Five? In a milonga three-and-a-half hours long with a class that overran by twenty minutes? May not have the intended effect.