[curmudgeon]

Prepositions are not easy to learn in a foreign language, so don't be despondent. Most prepositions in English have more than one meaning. It is also difficult to try and guess the correct usage. It is easier perhaps to learn the whole expression...in the morning, on Friday morning, at night etc.

I don't think there is a marked difference in AmE and BrE...where are you finding difficulty?