英语中，在某一时间前有时加介词有时不加，请问怎么区别和运用？

带有this和that指示词的时间,如this year, that time,不需要加介词

在带有this,next,last,one等时间状语前，不能加介词，这属于英文习惯用法。
e.g. this morning,this evening, next week,
next month, last night, last year,last Sunday,
one morning,one day etc.
其他一般要加介词:
e.g. in the morning/afternoon/evening
in January/February/March
in spring/summer/autumn/winter
in 2006/in the 21st century
on Sunday/Monday morning
on my birthday
on New Year's Day
on Christmas Day/Eve
at 11:30/20:40
at lunchtime
at noon/night
at Christmas