I don't think there is an answer on how long it can take for a story to be considered ready to be released from the hard drive. A couple of days? A couple of hours? Weeks? Months? Eeek, years?
It all depends on the story and with being honest with yourself. It's easy to think that a story doesn't need any more edits and rush it off to a magazine or a competition - I know because I have done it.
Last week, when I was meant to be using my writing time to continue with my novel, I wrote a story for a flash fiction competition - it took me a couple of hours to write, redraft and to feel happy with my story. I did leave it to the last minute to enter - the day before the closing date. But I left it until the final moments with the next story.
I have struggled with a particular short story for over a year. This was my Alice in Wonderland story with it's 'eat me' and 'drink' me - first it was a piece of flash fiction, then it grew and then it shrunk and then it enlarged. I sent it to magazines and got a few 'close but no cigar' responses and so I dumped it in my 'retired' folder. The other month I started to think about it. Why is it that when you're meant to be concentrating on one project that another retired project pops into your head?
I decided I wanted to enter it into a competition - I worked on it the day before the closing date. Went to bed, woke up and decided that the ending needed more work. But there was work, gym, food shopping and cinema in the way of me sitting down and finishing off the story. I had until midnight. I ended up frantically editing my story after my gym session and making the changes with 15 minutes of the deadline.
The one thing that I need to work on is deciding if I am going to enter a competition and then commit to getting my entry ready rather than spending weeks/months talking myself into and then out of sending an entry.