Aw, I can relate

. All I can suggest is getting only as close as he wants you to be by watching his body language, and step back and go away if he starts to look like he's going to take off or get freaked out. Use a lot of nice "hi's" and sweet talking with relaxed body language and no fast movements, even being careful not to lift your hands too high or too fast around him. Try not to even stare at him too long if you look at him in the face. Offer him favorite treats if he's interested, taking care not to give him too many extra calories lol. Positively reinforce when he does well with you. That's about all you can do. How long it will take for him to come around again depends on the individual personality I think. I know it's discouraging... keep your head up about it the best you can, and keep reinforcing the positive.
A few weeks ago, Don (Griffin already hates Don) had to rush into the room where the birds are, because their owner was off doing something else and not paying attention :54:... Thankfully he noticed Griffin was climbing into Robin's cage (very bad idea). Griffin has already lost 2 toenails in bloody accidents to Robin, but apparently the kid hasn't learned. Don frantically shooed Robin and Griffin apart, and chased Griffin down like a mad predator in attempt to get him away, then back in his cage. Long story short, there was a delayed reaction (a week or two later) he started the same panicked freaking and death screaming with me for no reason when I'd walk near him... not constantly, but he is still very far from being "right". No rhyme or reason to when the "switch" gets flipped on. We can be sitting and cuddling, when all of a sudden in a split second he'll look at me as if to remember the day a few weeks ago when "a human predator" had chased him and in his mind, tried to kill him. It breaks my heart and I had to leave the room so many times, not only to get Griffin to calm down, but so that he won't see my tears and how upset I get.
How long is it going to take for Jet and you? For Griffin and I? Even if we don't do anything to reinforce the negative again, it will just take as much time as THEY need to forget about it. How long that is just depends on the individual I believe. Griffin is not anywhere near as easy going as related species Robin is. In the 20+ years I've had Robin, he has unfortunately gone through a few traumatic experiences as you can imagine would happen in that many years, and Robin has NEVER freaked out for long, or ever held a grudge. His temperament is just different. Griffin is just as tame, but freaked out badly with what I would say is something Robin would have gotten over an hour later. They're all different.. Hang in there Grace!