To talk about an amount of time in Mandarin Chinese, we use the following nouns:

    鐘頭 / 钟头 – zhōng tóu – hour
    小時 / 小时 – xiǎo shí – hour
    分鐘 / 分钟 – fēn zhōng – minute
    秒鐘 / 秒钟 – miǎo zhōng – second

The measure word 個 / 个 (ge) is used when talking about hours, but minutes and seconds include the measure words 分 (fēn) and 秒 (miǎo), so no other measure words are needed.

Here are some examples showing how to talk about amounts of time:

我只有二十分鐘。
我只有二十分钟。
Wǒ zhǐ yǒu èr shí fēn zhōng.
I only have 20 minutes.

你每天看幾個小時的電視?
你每天看几个小时的电视?
Nǐ měitiān kàn jǐ ge xiǎo shí de diànshì?
How many hours a day do you watch TV?

一分鐘有六十秒鐘。
一分钟有六十秒钟。
Yī fēnzhōng yǒu liùshí miǎo zhōng.
One minute has 60 seconds.

我還要半個鐘頭。
我还要半个钟头。
Wǒ hái yào bàn gè zhōng tóu.
I still need half an hour.