There's a period of time which is beneficial. It's not about being secretive, it's about putting your head down and getting things done without interruption.
Five years is (in virtually any case) way longer than that should be. But three months? Great! Even a year, if you're really on to something. But after that you need viable interaction with your customers/users/prospects
I agree that time for heads-down coding is very important. My point was more about one's overall career -- that not contributing publicly to the industry can be detrimental.
Even if it takes a long time for your stealthy startup to launch, it can be beneficial to write about your experiences and/or open-source a cool project.
Five years is (in virtually any case) way longer than that should be. But three months? Great! Even a year, if you're really on to something. But after that you need viable interaction with your customers/users/prospects