The time between beta's is usually about a week, but it can vary. For a minor release, ie 3.x there are usually 2-3 betas. We will be releasing 3.2.0-b3 next, and after that it will likely be final release. The point of the beta's is to eliminate bugs though, and that's our goal. Our focus will always be on quality rather than meeting a predefined timeline.. so, things can change.