How long will someone be detained for violating a restraining order?

He will probably have to sit there for a week or so until a magistrate judge sees him. The judge will want to know why he's violating a court order. If the judge believes his answer, he will probably be released shortly. If your boyfriend is defiant and unrepentant, he could sit there for months... for contempt of court. The judge must protect the rights of the person that your boyfriend is bothering. There is no actual sentence time. Just as long as the judge thinks he needs to be there - and that he's assured that the person he's restrained from is safe.