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The ideal time to launch was yesterday, but that's already over. So the next best option is today, followed by tomorrow. There are very few apps/products where launching early with out a big marketing pitch will hurt. Judging by the fact that you are asking for advice here, I'm guessing you do not have a million dollar marketing budget.

It would be far better to launch now, get some initial users, improve your product based on their feedback and then really turn on the marketing effort. The key thing is to get started now, start getting users. Find out how they use your product, find out what they like or don't like.