Something finishes or ends by a certain time. When you finish something by a certain time, day, date, etc…you complete the action when the deadline comes. Use by with verbs that show one time actions or verbs that mean finishing or ending. Some examples are finish, end, complete, arrive, start, go, leave, etc. Use by plus one point in time:
- Please complete your essay by Friday
- Can you finish work by 6 tonight? If so, we can catch a movie.
- If we arrive at the station by 3pm we can catch the train.
- We have to start the meeting by 1pm if we want to finish at 5pm.