We sometimes use past tenses to describe things in the present or future that are imagined or unreal.
It's time we went.
We are using It's time... here to say that something is not happening, but it should be happening. Compare also the following:
Note that it's not possible to use this structure in negative sentences. We cannot say: It's high time you didn't depend on your parents any more. But we can use the construction it's time to or it's time for + object + to as alternatives to the unreal use of past forms to express this idea:
It's time we left. Our son will be home soon and he doesn't have a house key.
It's about time you started looking for a job. You can't depend on us all the time. It's high time you started to fend for yourself.
It's time for you to think seriously about what you want to do in your life.
It's time you thought seriously about what you want to achieve in your life.
It's time to reflect on how you want your life to proceed.
We also use what if and suppose/supposing + past simple to express a wish for something to be different than it actually is. Again we are using a past tense to make a suggestion for the future or to describe something that is imagined or unreal. Compare the following:
wish / if only
Suppose Henry came to stay with us for a couple of weeks. You'd like that, wouldn't you?
Supposing he wanted to live with us permanently. How would you feel about that?
What if I caught a later train? Then I'd be able to stay and help you finish the report.
What if you missed the last train? Then you'd have to sleep on my floor.
Similarly we can use wish and if only + past simple to express a wish for something to be different than it actually is:
Note that we also use wish and if only with the past perfect to express a regret about the past, a wish that something might have been different:
If only I could lose some weight. Then I'd be able to wear this dress.
If only I had more free time. I'm sure I'd be less stressed and more cheerful.
I wish I were younger. I'd love to be able to play tennis like Roger Federer.
I wish you could drive. Then I wouldn't need to be your personal chauffeur.
Note that the shortened forms of I'd had and you'd told in the above examples are abbreviations of the past perfect:
I wish I'd had more children. Then I wouldn't be so lonely now.
I wish you'd told me you felt lonely. You could've spent the summer with me.
I wish I had had more children. Then I wouldn't be so lonely now.
I wish you had told me you felt lonely. You could've spent the summer with me.