英语 in advance 和ahead of time . ahead of schedule. 区别.

in advanced应用于所有的语气，表示“事先，提前”的意思！
Tell me in advance! 提前给我说！

ahead of time这里有一个时间点，“在这个时间点之前”，比如俩人说好了八点见面，为了保险起见，一个会说：I'll phone you ahead of time to inform you. 我会提前给你电话提醒你的。

ahead of schedule 是比计划表或者安排表提前，具体可能计划好了施工进度，但是我们赶在了工期之前，可用：We finished the project ahead of schedule.

相比之下，后两者多用在比较具体的情形当中。第一个适用于大多数情况！

首先，三者都有“提前”的意思。

in advance 常置于句尾,常常是提前做某事。
例：It is cheaper if you book the tickets in advance.

ahead of time 强调的是提前了具体的某一小个时间段，
例：He arrived ahead of time, and had to wait.

ahead of schedule 强调的是比原计划，原进度提前了，句子的主题是一项任务类的事情
例：We finished the project ahead of schedule.

剑桥高级学习词典

in advance
in advance
before a particular time, or before doing a particular thing:
If you're going to come, please let me know in advance.

ahead of time
ahead of time MAINLY US
in advance:
Let's meet for lunch. I'll call you ahead of time to fix up exactly when and where.

ahead of schedule
ahead of schedule
early:
We expect the building work to be completed ahead of schedule.