Personally, I do not count the number of days that have passed since I post the question. When I think I have gathered enough responses, then that's the time I start to look at how much each responses affected me. There are times when it is so hard to choose the best answer, especially when you think of how much effort was given by a member to answer the question. There were also times when every perspective is so valuable I just want to select them all as best answers. This, perhaps, causes me to prolong the selection, as I keep on rereading the answers until I realize what best captures the idea that I'm looking for.
However, there were also times when I'll get the response I want right away but I still do not choose the best answer immediately because this will prevent other people from answering the question. I don't think many would still bother sharing their views if that will only equate to a single point so better leave the question open for answers.