I just left a comment at http://mathoverflow.net/questions/46949/justifying-the-definition-of-arclength as well about this, but that's no place to have a conversation. The question was open for about an hour when I found it and wrote my answer, but by the time I was finished (still about an hour after the question was asked) one of the previous answers had already been accepted. I left my comment and Steven Gubkin replied and wondered about the etiquette; conveniently, there is such a category here at mmo. (I have lurked around here for a while and thought I remembered there being such a thread already, but I can't find it.)

Of course, the person asking the question has every right to decide if it's answered, and certainly there are many answers (to other questions) which are virtually indisputably the correct ones. But it seems to me that so long as the question is open the answers can compete in the eyes of the OP and of the general audience, while once an answer is accepted, casual readership may drop.

In addition (if I may say this without an implied accusation) it seems dismissive of the answers that may come to accept one so quickly. One does not know what may turn up (I of course hope that what I write is valuable, or else I wouldn't write it). Steven Gubkin commented in response to me that he would change the accepted answer if a better one came along, but I don't want to try to steal the honor, nor do I want the previously accepted answerer to think that's what is going on. And if the award is transferable then wouldn't it make more sense to wait, say, a day?

So, is it bad etiquette to accept early? Alternatively, and less judgmentally, is it good etiquette to let it sit, and if so, for how long?

I'll repeat my comment on the question: it is in everyone's best interest to wait a day or so before accepting answers.

• The OP gets more views on the question, meaning both potentially more answers and (if you care about such things) potentially more upvotes on the question.
• A user who has posted an answer gets more views, meaning potentially more opportunities for correction and elaboration in the comments and (if you care about such things) potentially more upvotes on the answer.
• A user who has not posted an answer is more likely to post an answer which will itself be (if you care about such things) more likely to get upvoted.

At least, it can't hurt.

I agree that all other things being equal it is for the best to wait a day or so before accepting an answer.

Nevertheless I think it's really up to the OP. Sometimes you know as soon as you receive a certain answer that it is exactly what you wanted to hear, and sometimes (this is not a chronic problem for me!) you don't want to put off until tomorrow what you can do today. I think that quick accepters should not be specifically criticized.