COMPLETE THE IDEA Use “at” for very specific  times. Clock times for example. 

“In” is used for periods of time, so seasons or months or even longer periods of time like centuries or decades or years.

 In English we can use this preposition for specific descriptions of time. Most commonly with days of the week and parts of the week.

COMPLETE WITH THE CORRECT PREPOSITION OF TIME: AT, IN, ON

I'll be there at  dusk. 

I was born  in 1986. 

Let's have a coffee  on Friday morning. 

I’m going shopping  at lunchtime. 

It happened in  the 16th century. 

We're moving house on  Christmas Eve. 

I read my daughter a story  at bedtime. 

He'll visit them  in  October. 

I have an exam   on  my birthday. 

She's a little busy  at  present, can I get her to call you back? 

I finish the course at  the end of April. 

at  the moment, I'm working on a very interesting project.