When should I tell my family that I'm eloping?

My long time boyfrind, Ivan, and I have decided that we want to get married. I’m 18 and he’s 20. Yes we are young but we’ve been together for over five years and I can’t see myself with anyone else. My family hates him because he’s not their ideal for me and they refused to have any part in our future. We’ve already decided where and when and we know it’s what we really want. I’m just not sure when I should tell my family the happy news. I love him with all my heart. When should I break it to them?