This question already has an answer here:

Which one of the sentences below is correct?

  1. Please be ready by 5:00pm.
  2. Please be ready at 5:00pm.
  3. Please be ready on 5:00pm.

I'm really confused about this.

Can anyone explain all the sentences above please?

marked as duplicate by user3169, Em., JavaLatte, Glorfindel, ColleenV Apr 9 '17 at 12:21

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

migrated from english.stackexchange.com Apr 8 '17 at 13:16

This question came from our site for linguists, etymologists, and serious English language enthusiasts.


I will rather ask: Which one of the sentences below is not correct?

Unlike the very last one, the first and second ones (Please be ready by 5:00pm. and Please be ready at 5:00pm.) are both correct.

Take a look at the examples below:

  • She said to me: please be ready by 5:00pm.

In the sentence above, by 5:00pm connotes latest by, meaning: before 5:00pm.

  • She said to me: please be ready at 5:00pm.

Here, at 5:00pm translates into being ready at that very point in time, either: exactly 5:00pm.

  • She said to me: please be ready on 5:00pm.

In the last instance above, the sentence is grammatically wrong because the use of the preposition on is not appropriate.

In general, the preposition on is often used for places and or locations.

There is really no definite rule nor formula for choosing a preposition and this can be a tremendous challenge for English language learners.


Usually we use at with:

  • Clock times: "at 5:00 pm"
  • Mealtimes: "at breakfast"

We use in with:

  • Seasons of the Year
  • Years
  • Months
  • Part of the day

We use on with:

  • Days
  • Dates

We use by to express the end point of one activity

If you say be ready by 5:00 pm, it is the end time, not later than 5:00 pm.
Be ready at 5:00 pm is the correct expression (clock times).
Be ready on 5:00 pm is not correct: no days, nor dates after on.

English-Club Prepositions of Time

Not the answer you're looking for? Browse other questions tagged or ask your own question.