Sentences that begin with "until" or "not until" should be punctuated with a comma. I think it's awkward to structure sentences in this way but it isn't grammatically wrong. Not until he had finished his homework, did he go home. He went home until he had finished his homework. These two sentences have opposite meaning. The first says that he did his homework somewhere and then he went home. The second says that he finished his homework at home and then went somewhere. I would write "He didn't go home until he had finished his homework" Until the last minute of the match, we kept playing. Not until the last minute of the match, did we keep playing. (1） Not until the last minute of the match, did we leave. (2) (2) is closest in meaning but awkward. I would write: "We kept playing until the last minute of the match." or "We didn't leave until the last minute of the match" Not until they had the twins, did they feel they had formed a family They felt they had formed a family until they had the twins (3) They didn't feel they had formed a family until they had the twins (4) (4) is the closest in meaning and is how I would write the sentence. (3) has an opposite meaning. This sentence says that the didn't feel like a family after they had the twins.