'By then' definitions:

Definition of 'By then'

From: GCIDE

Then \Then\ ([th][e^]n), adv. [Originally the same word as than. See Than.]
1. At that time (referring to a time specified, either past or future). [1913 Webster]
And the Canaanite was then in the land. --Gen. xii. 6. [1913 Webster]
Now I know in part; but then shall I know even as also I am known. --1 Cor. xiii. 12. [1913 Webster]
2. Soon afterward, or immediately; next; afterward. [1913 Webster]
First be reconciled to thy brother, and then come and offer thy gift. --Matt. v. 24. [1913 Webster]
3. At another time; later; again. [1913 Webster]
One while the master is not aware of what is done, and then in other cases it may fall out to be own act. --L'Estrange. [1913 Webster]
By then. (a) By that time. (b) By the time that. [Obs.] [1913 Webster]
But that opinion, I trust, by then this following argument hath been well read, will be left for one of the mysteries of an indulgent Antichrist. --Milton. [1913 Webster]
Now and then. See under Now, adv.
Till then, until that time; until the time mentioned. --Milton. [1913 Webster]
Note: Then is often used elliptically, like an adjective, for then existing; as, the then administration. [1913 Webster]