By The Time Meaning

(idiomatic) When.

Example:   I'll be an old man by the time you finish!‎
1898, Winston Churchill, chapter 5, The Celebrity:
  But Miss Thorn relieved the situation by laughing aloud, […] . By the time we reached the house we were thanking our stars she had come. Mrs. Cooke came out from under the port-cochere to welcome her.