如果By the time 引导的句子用一般现在时，主句应该用将来完成时（如果是 be 动词，用一般将来时）；如果By the time 引导的句子用一般一般过去时，主句应该用过去完成时（如果是 be 动词，用一般过去时）。例如：

    By the time you come back, I'll have done my homework.在你回来以前，我的作业会都做完的。（摘自赵振才编著：《英语常见问题解答大词典》增订版第五版 p.225）

    By the time I got to the station the train had already gone.我到达火车站时，火车已经开走了。（同上）

    I'll be in bed by the time you get home. 等你到家时我已经上床睡觉了。/ By the time that the guards realized what was happening, the gang were already inside the bank. 等到保安明白过来出了什么事时，劫匪已经进了银行。（摘自《牛津英语用法指南》第四版414.1）