You can turn off beta updates at any time, but you will not get a Release Candidate, which is still a beta. If turned off, you will still get 26.0 General Release when it is available (even if you didn’t go to an RC first), but you will be waiting a week(-ish) longer than the RC beta. If you want off the beta train, I would recommend installing the RC and then turning betas off. You may still have a GR update and maybe even a 26.0.1 update if there are any issues when released, but it will most likely be minor. You won’t be part of the 26.1 beta then, which will most likely mid-to-late September. So you will most likely get 26.1 in late October when it is General Release.