Am I the only one that has listened to a setup and immediately thought "Wow, this is good" only to realize days later that I've been turning on my music but not listening for very long when I did. And then a week or so after that I notice that I'd go entire days without turning it on at all. I've learned not to trust my initial reaction in a comparison.
My experience is generally the opposite. My first impression always sticks. I'm a "tone/timbre" first guy, so voices and instruments I like have to sound "right" to my perception - invoke certain "colors" in my mind - and that is pretty immediately the case or not. If I think "wow that acoustic guitar sounds RIGHT, I can accept that as an acoustic guitar, not some electronic deviation" then we are off to a good start and most other instruments will likely sound good to me. I've yet to have such an impression reversed over time.
The closest experience I've had to what you mention had to do with amplifiers. (And if this triggers certain folks I don't give a damn...)...
A couple times my CJ tube amps were out of my system for quite a while. And at that time I'd been using some little Thiel speakers that I'd always loved. I used a solid state amp for that time (can't remember if it was my Bryston or Harman Kardon). As the weeks passed I noticed I wasn't listening as much. I wasn't transfixed by the sound as I was normally. Gradually my dedicated listening petered out to nothing. I actually thought "maybe I'm over the whole music listening/2 channel thing." So I was thinking of selling my more expensive gear, starting with the CJ tube amps. I got them fixed (it was just a fuse in the end) to sell them, put them in the system just to make sure they were working fine and..bam!..there was "that" sound I'd been missing. More organic, rich, beautiful, convincing...I could not get my butt off the chair. Day after day I couldn't stop listening and realized I actually did still love listening. Amazingly, it happened again, years later when I didn't have the CJs in the house and used my Harman Kardon amp. Again, not expecting it but I found my listening trailed off over time and again...thought I must be losing interest. But I ended up borrowing a little Eico tube integrated when the Harman died on me, and again, as before, that rich sound was back and I was back to being transfixed in front of the system. (I ended up buying an Eico for myself, as well as getting my CJ amps back in the system).
The upshot for me was: no way in hell am I letting go of these amps! A Golden Eared purely subjectivist audiophile would at this point declare "It's obvious that what I thought I heard was true! My ears don't lie!" That is NOT my position. My position is that it's plausible the tube amps altered the sound in a subtle way that I found significant. But it's also very possible that sheer bias effects played a big role in the above stories. But I can justify keeping the amps because even if it's purely a bias effect, it has proven to be such a strong one, and a reliable one year after year, that I am fine availing myself of that effect. I just wouldn't go trumpetting to others that they need to conclude anything dubious on what I have described.
Oddly, it has rarely happened the other direction, where the first listening results in not liking it and the long term changes to liking. And there have been plenty that I didn't like from the start and even after time I still didn't enjoy. I can only think of one that broke through that barrier.
Likewise: I've never gone from not liking a speaker to liking it later on. And I've had lots of opportunity to hear the same loudspeakers in various places at different times.
One of the speakers that I bought to try out were the Audio Physic Scorpios. I had loved the tone of the two previous AP speakers I'd owned so figured this was a good bet. But despite that they did tons of great things in terms of disappearing, soundstaging, sounding punchy, vivid...their tone and timbre with instruments just never convinced me, never sounded "right." Over many months I never acclimated and that perception never changed, so with disapointment I sold them.