For me it's after 2-3 weeks. After 2 weeks the central nerve system is being formed and after 3 weeks the heart starts to beat. That's enough to qualify it as human.
Whether or not it has rights by then is a different matter alltogether. There are plenty of fully grown adults on this planet that don't have rights....
BTW since my option isn't available in the poll, I voted for the 1-month option.