Do you have advice for the owner of a very timid cat?

I adopted this very shy but friendly cat from the SPCA 2 weeks ago. I call him “Uahi” (Hawaiian for smoke). I was told that he’s 3 years old but my veterinarian thinks he’s half that old. Veterinarian said he’s healthy. He eats, drinks, poops/pees (in litter box very well).

He has shown no aggressive behavior (snarling, hissing, catching or biting) to me or my other male cat (They touched noses and pretty much ignore each other.

I’m retired and spend at least 4 hours a day with him (when I can get him to come out of his covered bed). The best times are in the morning and at night.

The least little thing will freak him out. Like rain on the roof, the sound of a door, toilet, a broom sweeping the floor. He also panics for no apparent reason at all. During which times he darts back into hiding and won’t come out for several hours.

For short periods he can be very friendly butting his head into me, rubbing against me. But no purring at all. Sometimes he will play with a toy mouse and feather on a string toy.

I let him do anything he wants to do. Unfortunately he mostly wants to hide. I tried to bribe him to come out of hiding with special cat treats (he won’t touch them).

I’ve never seen a cat so shy. I’m trying to get him to relax with very little progress. Every day it’s like starting over. It’s like he forgot about all the fun things that we did together the day before.

Any suggestions? Ideas?

Might he be less shy in a year?

Is this as good as it gets?

Thank you.