Not only is it ok to answer your own question, but there's no need to wait at all. In fact, the interface even suggests answering immediately:
If you have an answer, please share it. If you would like additional answers, feel free to say (in a comment or in your answer) that you're looking for improvements. Even if you don't say something like that, it's an open question and people are free to add answers.
When I answer a question and then the OP comes along and posts a self-answer that he had all along, I sometimes feel a little like I've wasted my effort -- why did I spend time on that if he already knew what I posted? (Only a little, because I still, I hope, helped make the Internet a better place, but still...) Granted, if you never post your answer others will never know that, and I would say that if you delay you should only post if you have something new to add. That's the price you pay for not offering your answer up front -- you might not get to offer it at all.
If you want to wait to see what others come up with first, I would suggest waiting until you get some answers (that might be right away or not for a while), or, failing that, a couple days. Once the question is off the front page it's less likely to gain answers, so that might be a good time to come back to it.
Finally, you can signal that you still want answers by not be accepting your own.