Es ist höchste Zeit (It's high time)

To ask the time in German, you can say: (Nach der Zeit fragen)

• Wie viel Uhr ist es?
• Wie spät ist es?

The hour is divided like a pie in four quarters (Viertel) and two halves (halb)
For "half past," you say "halb" and the next hour. "Halb fünf" = 4:30, i.e., half (way to) eight.
After is "nach". "Es ist zehn nach zwei" = 2:10 (It's ten after two).
For "quarter past," you say "Viertel nach": "Viertel nach neun" = 9:15.
To or before is "vor" (pron. FOR). "Viertel vor zwei" = 1:45. "Zehn vor elf" = 10:50.
English "o'clock" is "Uhr" in German. "Es ist fünf Uhr" = 5:00 (five o'clock).
The word "Uhr" has two meanings: "o'clock" and "watch". So if you want to ask if smbd has got a new watch, you say "Oh, eine neue Uhr?"

Germans do not add any specifications as "am" and "pm", but as they very often (timetables, TV guides, store hours) use 24-hour ("military") time, you can easily understand what part of the day is meant. Add 12 to a pm time to get the 24-hour form: 2 pm + 12 = 14.00 (vierzehn Uhr).