Wish does not take the tense of the real world. It takes one step back.
The step back
For something you want to be different now, use wish + past simple. I wish I had more time. I wish I knew her name.
Not last week
Had and knew look like the past. Here they talk about this moment. The past form means: this is not real.
I wish I have more time. — no
I wish I had more time. — yes