If only one parent has lopped ears it is highly unlikely they will lop. That being said my first Lionlop babies had ALL lopped ears, mom was F1 SM lionhead(unknown breeds behind) with shortish up ears and the dad was a a big holland lop with mini lop type - huge wonderful crown, amazing ears and head, ect. You are more likely to get loppies at generation two.
I have my first purebred holland litter in two years right now! They are three weeks and their ears are already air plane, it started at 2 1/2 weeks. It depends. I have saw ears drop as late as 6 months and rabbits who switch things up all through their life - left up and right down, both up, left down and right up, air plane, both down, ect.