By the time he finally felt the land under my feet, he was tired out.
1) by the time 等到；到……的时候
The kind man man had gone by the time I woke up.
当我醒来时，那个好心人已经走了。
2) be tired out 筋疲力尽
He was tired out after his long trip to Yangzhou.
至扬州长途旅行归来后，他觉得非常疲倦。
