Men and women both, but especially women, and doubly-especially young women, should know what to look for, and the best place to get that information is from a rape and abuse crisis center. Abuse can take so many forms, from maybe just humiliating comments to start with, and then maybe controling what one does and where one goes and who one knows, and then maybe shouting, then yelling, then swearing and other bully-tactics, and if verbal abuse does not get the abuser what he/she wants, physical abuse is just a click away.
But for the young woman, say 16-25 years old, she will see these changes and escalations in her man, but will deny the growing danger she might be in, and will defend him; it might take years for her to truly see and admit to herself where her relationship is going, and has gone, and that it will not likely change.
So, to answer "How long must one take abuse?"
That is tough to answer. First get educated.