As I understand it, in order to get UK citizenship, you have to spend some time in the UK on other visas first, plus x days each year in the country. Assuming you have the right visas, and spend the right amount of time in the UK, and don't have any other complications, how long does it take from start to finish?
It's the same as getting normal citizenship.
From the UK Government site on citizenship:
You can apply for British citizenship by naturalisation if:
- you’re 18 or over
- you’re of good character, eg you don’t have a serious or recent criminal record
- you’ll continue to live in the UK
- you have met the knowledge of English and life in the UK requirements
And you must usually have:
- lived in the UK for at least the 5 years before the date of your application
- spent no more than 450 days outside the UK during those 5 years
- spent no more than 90 days outside the UK in the last 12 months
- been granted indefinite leave to stay in the UK (or permanent residence if you’re an EEA national) - this means there’s no specific date that you have to leave
- had indefinite leave to stay in the UK for the last 12 months (or permanent residence if you’re an EEA national) not broken any immigration laws while in the UK
However, there are different rules if your spouse or partner is a British citizen (links are on same page).