Thake this rule :
at - on - in
We can use these time phrases in the present and future .
at + time & two or three days .
time: at 7 o'clock
at christmas .
on +day & date
on july 2 nd.
in + month & season & year / dacade / century .
month= in june
in the twenty-first century.
We don't use a preposition with last and yesterday .
We went there last year/ yesterday .