Three o'clock (san-ji). Depending on context it can be 3 AM or 3 PM, though in everyday speech it often means 3 PM; can be used adverbially (e.g., at 3 o'clock).
会議は３時に始まります。
The meeting starts at 3 o'clock.
明日は３時に駅で待ち合わせましょう。
Let's meet at the station at 3 tomorrow.
３時になると子どもたちは学校から帰ってくる。
At three o'clock, the children come home from school.
午前３時に出発するので、早く寝ます。
We leave at 3 AM, so I'll go to bed early.
The afternoon snack eaten around 3 PM — commonly called 'san-ji no oyatsu' in Japanese.
子どものころ、毎日３時におやつを食べていた。
When I was a child, I ate a snack every day at three.
午後の仕事の合間に軽く３時のおやつをとった。
I had a light 3 o'clock snack during a break in the afternoon work.
In Buddhist terminology, 'the three ages' (san-ji) — the three eras after the Buddha's death: the age of the true law, the age of the semblance of the law, and the degenerate age. This is a specialized religious sense.
仏教では正法・像法・末法の三時という考え方がある。
In Buddhism there is the concept of the three ages: the true law, the semblance of the law, and the degenerate age.