I'm guessing you're thinking of immigration visa time in UK before eligibility to ILR (Indefinite Leave to Remain)

These days the normal immigration journey is 5 years to ILR with a 'mid-term' FLR visa needed at after 30 month.

If you enter UK as Fiance then you'll need to get married/civil partnership before applying for the first FLR which lasts 30months then apply the second FLR for the final 30 months before application for ILR