The past tense in English is sometimes used not for the past, but as an unreal past. This means that the unreal past is used for situations that are unreal, usually in the present but also in the future.
We typically use the unreal past to indicate that what we are talking or writing about is something we wish for or is something hypothetical, imagined, a preference, or to be polite.
The unreal past is used:
after conditional words and expressions like if, supposing, if only, what if;
after the verbto wish;
after the expression I’d rather.
Conditions
Supposing an elephant and a mouse fell in love.
What if we painted the room yellow?
If you went to the movies, I would babysit.
If only I had more money, I could go to the movies too.
Wishes
I wish I had more money.
She wishes she was beautiful.
We wish we could come to your party.
I wish I hadn’t said that.
He wishes he hadn’t bought the car.
Preferences
When we want to talk about a course of action we would prefer someone else to take, we useI’d rather + past tense.
I‘d rather you went to the party with me.
He‘d rather you called the police.
I’d rather you didn’t hunt elephants.
In speaking, the stress can be important in these sentences, to show what our preference is:
I’d rather you went. (instead of me)
I’d rather you went. (instead of staying)
He’d rather you called the police. (instead of me)
He’d rather you called the police. (instead of the firemen)
Similarly, when we want to say that now is a suitable moment to do something, either for ourselves or for someone else, we useit’s time + past tense.
It’s time you paid that bill.
It’s time I went home.
Don’t you think it’s time you had a haircut?
In the exam, they will only give you one hint of what to use, so it’s important to analyze the sentences carefully to decide which expression best fits the situation.