How long you need to permanently reside in the UK to obtain ILR depends on two factors:
Subcategory – holders of an Exceptional Promise visa need to wait until they complete 5-year continuous residence in the UK;
Field of expertise. The UK values top-class academics, innovators and researchers. If you are an established leader with an Exceptional Talent visa in one of these fields, you should complete 3 years of continuous residence in the UK to obtain ILR. Established leaders in the fields of culture, arts and IT are eligible to apply for ILR after 5 years.