ROA is a settled status. It is the same as having Citizenship apart from not having a British passport. It is primarily used by those who wish to continue to use their own nationality passport rather than a British one, there is no qualifying period, as far as I know, as they have an automatic right to Citizenship.
Do not get confused with Permanent Residency.
Over the years there have been many types of British passports issued, which is a bit of a minefield regarding right of stay in the UK, these are slowly being removed.
For example you had British Dependent Territory Citizens: British Overseas Citizens: British National Overseas Citizens: British Protected Persons.
The second and third examples did not have an automatic right to stay, in fact BNO had to qualify for entry like any other foreign national