Releases are generally available immediately to devices set to use the Alpha channel. If the release works well for Alpha users, it is likely to be released in a day or two for devices set to use the Beta channel; if that goes well it will likely be released to the Stable channel soon after. You can see which channel your device is set to use via "Settings", "System", "System update".
Note that downgrade protection means that if you switch channels to try out a new release you won't be able to switch back to the older GrapheneOS if you don't like the release you got via a faster channel. Neither switching release channels nor sideloading an older OTA image will work, so the earlier-access channels may be best for second devices or adventurous individuals.
Please note that I do not speak for the GrapheneOS project.