1. Local PC
Basically, they can be used for 1-3 weeks after the latest version is released. Although pre-release beta versions are not officially supported, they can work often. Try this out using the beta version, and if a problem occurs, we shall provide support and investigate the issue as much as we can. Please note that it can sometimes be difficult to resolve such issues for the short term especially when it comes to a beta major version.
2. Cloud Devices
Basically, they can be used for 3-5 weeks after the latest version is released. We shall always provide major versions, but we shall provide every 2 or 3 minor versions. For example, suppose we provide iOS 15.0, we'll provide iOS 15.2 or iOS 15.3 cloud device while we won't provide iOS 15.1.
We are not currently providing pre-release beta versions (we plan to support these in the future).
3. External Cloud services (BrowserStack/SauceLabs)
This will be possible in cases where the latest version is provided by an external service. The same is also true for beta versions.
The period during which the beta version or latest version is supported depends on the service, but this is often within 1-3 weeks after it becomes usable.