I have seen some examples about using "in" with time expressions. They give some examples as shown below:
I will leave for vacation in a month. (Exactly one month from now I will go on vacation.)
We’ll be there in an hour. (Exactly one hour will go by and then we will arrive.)
But these comments confused me. Then I looked the usage of "in" up in a dictionary and it says about usage of "in" with time expressions :"before or at the end of a particular period". I think the comments and the definition in the dictionary contradict each other?
I have examples of mine:
1- Dinner will be ready in ten minutes. (Maybe dinner will be ready at the 5th minute? or 8th. Does it strictly mean dinner will be ready at the end of the ten minutes?)
2- My letter arrived in two days. ( Does that mean it took exactly two days to arrive? or Could it be just one day because he/she doesnt remember the exact time?)
3- Imagine you are on the first day of a month and your friend says: I will be going outside the country in this month. (Does that mean he/she could go tomorrow or ten days later or at the end of the month?)
4- He can run a mile in 5 minutes. ( Does that mean he has to spent entire 5 minutes to run a mile? Could it be 4 or 4.5 minutes?)