They use more of a American English on duolingo. But they try to accommodate for both so "Its A quarter to eight" may sound odd in America but maybe its an alternate solution.

I'm American and I hear and use both "quarter to" and "quarter of eight" frequently.

Because when telling the time, you say literally "the hours are..." "le ore sono..."

:)

Native speaker of American English here, but "quarter of" always confused me. I mean, a quarter of eight sounds like it should more literally mean 7:15, so I always use "quarter to" instead.

Because 'otto' is actually plural. 8 being greater than 1. It's basically when telling time it's nearly always le + number. One is different. See http://italian.about.com/cs/travel/ht/telltimeitalian.htm for details

Time in italian is usually told as "Sono le number" like "Sono le otto" similar to how we say "It is eight". Except in italian when using numbers (higher than 1) they use the plural "sono" instead of "è".

Sono le otto = it's eight

meno un quarto = less a quarter

Note: It's "quarto" (quarter or 4th) not quattro (4)

I guess literal translation is "The (hours) are eight minus a quarter"