by: time

Not later than

By can mean ‘not later than’.

• I’ll be home by five o’clock. (= at or before five)
• ‘Can I borrow your car?’ ‘Yes, but I must have it back by tonight.’ (= tonight or before)

By can also suggest the idea of ‘progress up to a particular time’.

• By the end of the meal, everybody was drunk.

Before a verb, we use by the time (that).

• I’ll be in bed by the time you get home.
• By the time that the guards realised what was happening, the gang were already inside the bank.

note

For the difference between by and until, (see here).

Other meanings

By can also be used to talk about time in the rather literary expressions by day and by night (= during the day/night).

• He worked by night and slept by day.

Note also day by day, hour by hour etc.

• The situation is getting more serious day by day. (= … each day.)

And one can pay by the hour, by the day etc.

• In this job we’re paid by the hour.
• You can rent a bicycle by the day or by the week.