There isn't a specific amount of time. No one is a good person by default. Regardless of one's actions, if anyone were to be a good person, they would have no sin in their heart. It's through God that we are made holy, but only He is truly good.
A person who has no sin in their heart is not automatically a good person. A good person is anyone who is accepting and kind, a good person doesn't judge others' differences and a good person treats everyone equally.
