When are you eligible to apply for settlement / indefinite leave to remain?

When you are eligible to apply for settlement would entirely depend on what category the applicant is applying under. Most have a 5-year or 10-year route to settlement. For example, most PBS categories that lead to settlement require you to complete 5 years, whereas applications made as partners or parents have 5-year and 10-year routes. The long residence category requires you to demonstrate that you have had continuous and lawful residence for at least 10 years; it doesn’t matter what category this leave was granted under.