Usually we would want to release the first alpha of a new version as
soon as practically possible after branching. However, in case of S3_1
I'm for postponing S3_1-alpha1 a bit. We have not yet released
3.0.0-beta1, and the latest thing out from S3_0 is alpha5. I don't
want alphas from multiple branches to exist simultaneously. So the
planned S3_1-alpha1 time is soon after 3.0.0-beta1 release.
Even if we're not making alpha1 just yet, remember that branch is
about stabilizing a version. New features should go to master only,
unless there's a justified reason to include them to S3_1 too.