Not until 引导时间状语从句放在句首时，主句必须用倒装结构。如果从句谓语动词是一般过去时或者过去完成时，主句应该用一般过去时。例如：Not until the clock struck 12 did he go to bed . 钟敲了12下后他才上床。/ Not until all the demands had been turned down did the workers decide to go on strike . 一直到所有的要求遭到拒绝之后，工人们才决定罢工。（《薄冰英语惯用法词典》）    until 与 till 常可换用 ， 但 until 用于句首时不可换用 till 。 until 比 till 正式。until 所表示的时间长久 ； till 则表达时间的片刻 。 例如： You must stay in bed until your temperature is normal . 你必须在体温恢复正常后才能起床。/ Until she was sixteen she had never be away from her native village . 她在16岁以前从未离开过老家。 （《薄冰英语惯用法词典》）