Next pre release(alpha2 or beta) date of 5.0

Hello.

does anyone know about the next pre release (alpha2 or beta) date of 5.0 in approximate.

it is ok that not accurate.

I am started to working on a new product based on elastic stack and have to choose e.s. version.

You really should not be using a pre-GA build in a production system!!! There are no guarantees any alpha/beta will be compatible at all with 5.0 GA

Of course I know pre-GA is not applicable for production, also pre-GA will not compatible with GA.
But I considering develop my BETA product with pre-GA and Expect that at the end of the developing I could replace with GA a few month later.
So I am concerned about the next alpha, beta release forecast.