how to use on/in & at

They arrived at 5 o’cock.
They arrived on Friday.
They arrived in October. / They arrived in 1968.

at : 
often use with TIME at 5 o’clock at 11.45 at midnight at lunchtime at sunset v.v... 

on :
often use with DAY on Friday on 12 March 1994 on Christmas Day on my birthday

in :
often use with  BIG TIME ( months/years/seasons): in October in 1968 in the 18th century in the past in(the)winter in the 1970s in the Middle Ages in (the) future


I don’t like going out at night.
Will you be here at the weekend?
Do you give each other presents at Christmas? Mr Benn is busy at the moment / at present. Liz and I arrived at the same time.

in the morning(s) in the afternoon(s) in the evening(s) I’ll see you in the morning.
Do you work in the evening? on Friday morning(s) on Sunday afternoon(s) on 
Monday evening(s) v.v... 
I’ll be at home on Friday morning. Do you usually go out on Saturday evening?

The train will be leaving in a few minutes.
Jack has gone away. He’ll be back in a week. (= a week from now)  
They’re getting married in six months’ time. (hoặc ...in six months.)  
I learnt to drive in four weeks. (= It took me four weeks to learn)