"Good morning, it's seven o'clock."
I was confused between the reading of 七 as 'shichi' vs 'nana' (7). Likewise 'shi' vs 'yon' (4), and 'ku' vs 'kyu' (9). There is some discussion of it here: https://japanese.stackexchange.com/questions/328/how-to-choose-between-%E3%82%88%E3%82%93-yon-vs-%E3%81%97-shi-for-%E5%9B%9B-4-and-%E3%81%97%E3%81%A1-shichi-vs
From what I have gathered there is an evilness to do with numbers. The way they are pronounced depends on what they are counting. Also many kanji have different readings (pronunciation) depending on whether they are the kanji on its own, with another kanji, or with hiragana or katakana.