I had some sessions years ago for anxiety- which is not what I actually went for but the woman fancied herself a bit of a therapist and decided that we should start with anxiety and I waa insufficiently assertive ij those days to say no.
The first session was kind of crazy. I didn't really believe in it (or more specifically that it would work on ME) but I recall remembering nothing between her starting and it being an hour later.
I had severe social anxiety back then, especially about crowded places. There was a work event in the city at a bowling bar that night (not a bowling alley - think a trendy bar that happens to have four bowling lanes). Normally I'd have made an excuse, but I went. And I had fun. And I ended up bowling a few frames with some total strangers. Every single thing about that night was nothing like me.
I still don't love a social situation, but it's never been as bad as it was before that session.
I had a further session but I was physically uncomfortable in the chair and that was distracting and definitely didn't have the same effect. No time slippage, nothing but being aware of the physical discomfort.
So all that being said, I believe it can work, but I think both the hypnotherapist and the environment are important.
I have heard the details of Walkers experience and it sounded utterly bizarre so I'm unsurprised it did nothing for him.
I was not paying for mine and to have it covered the hypnotherapist had to be accredited by some regulating body. My recommendation would be to research a good practitioner first.