staged rollout means that you roll a new version to a percentage of users and you then increase that percentage over time. The reason is to catch bugs in a new version early before they reach a large part of the userbase.
In staged rollout, you choose first the percentage of users to roll to. The specific users that will get the new update are chosen randomly on each update.
You can optionally narrow the rollout to specific countries, but we don’t do that.
So with Sleep as Android, every staged rollout is distributed completely randomly.
To get updates first, you can join the betatesters group. That of course comes at a tradeoff of receiving not perfectly stable version.
To join beta, see https://docs.sleep.urbandroid.org/faqs/get_beta.html