Meaning/Usage: When you want to express that you waited a long time. A synonym of this would be, "finally."（当你想表达你等待了很长时间的时候。这个词的相近词是“最后”。）

Explanation: When you wait for something, the time on a clock is the biggest factor.

"It's about time."
"It's about time. I waited two hours for you."
"It's about time I got a chance to play."

A: "I've been waiting for 3 weeks to try out the new laptop. Isn't it my turn yet?"
B: "Yes. It's your turn. I'll get it for you."
A: "It's about time."