If you tell a friend,"it's high time you learned how to drive," this means that your friend doesn't know how to drive yet, and you're suggesting that your friend really learn how to drive now. If you tell someone,"it's high time I got a raise at work," it implies that you have been expecting a raise for some time, and you're saying that your boss should really give you a raise now. It's high time gives the idea that something is overdue and that the activity should have happened already.
I hope you noticed that it's high time is followed by a clause. Remember that a clause always has a subject and a verb. Also notice that the verb in the clause is in the past tense even though you're talking about the present and the near future. For example, a mother might tell her teenaged son, "it's high time you went to bed." She means he should really go to bed now. The mother might also say, "it's high time you opened a savings account." She means he should really start putting his money in the bank now or the very near future.
This is similar to the structure of a second conditional clause (remember? "If I were rich" means I am not rich), as well as when you wish about the present or the future. I wish I had a boat means I don't have a boat right now. When you say, "It's high time you bought a house," it means I really think you should buy a house, and in the right context, it could also mean "I really wish you would buy a house."
A: So what are your plans for the summer?
B: I'm thinking of taking some cooking classes. It's high time I learned how to cook.
A: That's a great idea. My sister studied at the Culinary Institute. She said she learned a lot.
B: Oh yeah? What about you? What are you up to this summer?
A: Well, I thought it was high time I checked out London, so I'm planning a trip there.
B: Really, you've never been?
B: Yeah. It's definitely high time you went.
Now, it's your turn. Try making your own sentences. What should you start doing now that you've been thinking about for a long time?
Is it now time for you to buy a house? You can say, "It's high time I bought a house."
Is it now time for you to take a vacation? -- It's high time I took a vacation.
Is it now time for you to start working out? -- It's high time I started working out.
Is it now time for you to organize your apartment? -- It's high time ...
You get the picture.
a raise - an increase in salary
overdue - late (overdue book at the library; overdue payment)
context - scenario, situation
What are you up to? - What are you doing?
working out - exercising
I hope you all had a nice weekend. Have you been using our expressions in your conversations? If not, it's high time you did. Speak English as much as you can.