Sorry, but the correct interval is forever. You should not repost on Stack Overflow/Exchange.
Editing bumps your question to the top of the "active" lists for its tags, and to the front page of the site; both of these are high-visibility areas where many people eager to answer your question are hovering. You can also (when you have enough reputation) tack a bounty onto your question, which will put it into a "featured" section for a week, with a bigger carrot held out for those answerers. More details can be found at How do I get attention for old, unanswered questions?.
You should certainly do your best originally to post an interesting and descriptive question, but the edit feature is there for a reason. Don't hestitate to update your question with more details or even a partial solution (though please refrain from pointless minor "BUMP"s).
You're right that the time of day does have an effect on the answers you'll get. There's absolutely nothing wrong with holding off on editing or posting until a time when you know site activity is high, or perhaps even when you've seen a particular user who you think would provide a good answer hanging around (although of course you can't guarantee that person will answer).
As an aside, if you have actually solved your first problem and have a follow-up question to ask, that's perfectly fine. Just make it clear that you are asking about another aspect of the same issue.