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Would someone please help me understand the difference between [1] and [2]?

[1] We are in the summer break.

[2] We are on the summer break.

Best wishes,

Hiro
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Comments  (Page 2) 
Lakshwadeep2. "at", "on", and "in" are all used for prepositions of time, but each are used in different ways.

"at" is specific to roughly the minute/second (at 10:30, at noon-means 12:00 not the entire hour)

"on" is roughly a day or date (on Monday, on the weekend, on New Year's Day)

"in" is nonspecific during a certain time frame(in two minutes/days, in winter, in January, in 2008)

Your examples are correct but the use of prepositions in temporal contexts is far more complex than your rules indicate. For example, You can see the stars at night refers to the entire night, not just a minute or second. I don't want to go out on cold mornings doesn't refer to an entire day or date.
In the night and by night are also used.
CB