Being keto (fat) adapted is a highly individualized thing, IMO. How much time it takes sort of depends on the state of your metabolism when you start, the level of carb restriction that you follow, and other factors unique to the individual. When I started I was morbidly obese times 10, I was a type 2 diabetic, and I had high blood pressure. I was totally insulin resistant. My metabolism was a disaster. I'd done low carb diets on and off for decades, but cheating was always part of my diet plan. Only this time did I choose to make this a permanent WOE. When I made cheating not an option everything clicked and I started receiving the full benefits of this WOE. Doing keto right paid dividends. I found the success that I'd longed for since the weight started piling on in the early 1990's.

I find it difficult to answer your question even as it applies to me. I don't know that I can really define when I became keto/fat adapted. I did notice some "stages" along the way after I went all-in with this way of eating (i.e. no cheating - LC everyday). Here is what I recall happened...

I started with a diet plan of less than 30 net carbs per day. For me at my size that was well within the keto zone for me.

As is typical with a very low carb diet I lost a significant amount of water weight in the first 10 days and suffered from symptoms of keto flu (felt crappy, lack of energy, etc.).

Within two weeks I was over the keto flu thing and feeling better. High blood sugar from diabetes had me feeling wiped out and lethargic in the months before the diet, so by switching to low carb my blood sugar stabilized and my energy levels returned to normal. 3 weeks into this WOE I was feeling much better, much healthier. I had a reasonable amount of energy for someone who still weighed more than 400 pounds. I still had carb cravings and it did take willpower to stay on plan those first few weeks, but I managed to do it.

The period between 2 weeks and 6 weeks was my honeymoon period. I liked the food I was eating. I was feeling better. I was losing weight. Everything was going great. THEN as time went on the food boredom phase kicked into gear. I started getting tired of the food I was eating; really tired of it. The thought of eating another egg, another salad or a piece of meat or cheese or green beans, etc., practically gagged me. The pull to dive back into the carbs really intensified. I did not give in. I stuck to OP foods no matter what. If necessary I would eat more OP foods than usual, even going over my carb count an a given day to keep me from diving into the junk. For me this was the hardest period in my transition to this WOE.

At about 3 months into the diet some magic started to happen. I started getting fidgety from sitting too long. I felt compelled to get up and move more. At the same time my appetite started to plummet. I was eating low carb those first few months, but I was eating a ton of LC food. Almost overnight I started not wanting to eat so much. I then had a week of terrible insomnia and when that ended I'd morphed from a night person who loved to sleep in on weekends into a morning person who goes to bed early and wakes up with the sun. I had never been a morning person for my entire life, then suddenly I was and I've been that way ever since. This period, about 3 months into this WOE, is when I think my metabolism started functioning properly. I was eating less, waking up early, and I had a tremendous boost in energy. At 375 pounds I started a regular walking regimen. I was compelled to be more active as if I didn't really have a choice. My active lifestyle continues to this day.

After about the 4th month of 100% OP eating my cravings for carbs, including fruit and other old favorites, started to fade. The pull to want them started to disappear. At the same time the LC food boredom phase came to and end. I stopped missing the foods that I no longer ate. I started enjoying the LC foods I was eating more and more each day. LC foods that could hardly choke down just weeks before became my new favorite foods. I think this is when my carb addiction started to break. My brain was letting go of the desire for carbs and rewiring itself around my new WOE. At this stage of the game my "diet" stopped feeling like misery and deprivation. The "diet food" was simply becoming the normal, everyday foods that I eat. It was at this point that I knew that I could sustain this WOE for the long haul. I still had fond memories of junky old carbs, but the pull to eat them slowly came to an end.

At 9 months into LCHF/keto I'd lost around 100 pounds. But my rate weight loss began to slow down. I began to work on bad habits (snacking) and introduced intermittent fasting into my regimen to help keep the scale moving. At about this time I start checking my blood sugar on a regular basis and was surprised to find that it was still higher than normal. My fasting blood sugar was still at prediabetes levels. I was controlling my diabetes through diet, but it was not cured. Even just a few too many carbs in a meal could shoot my blood sugar to unsafe (damaging) levels. Then suddenly - over a matter of a few weeks - my blood sugar normalized. My fasting BG fell from at or around 110 to being between 75 and 85 on most days. My insulin resistance appeared to be resolved. After that shift in BG I could tolerate more carbs in my diet without high spikes in blood sugar. IMO, I'd reversed my diabetes. Some sort of healing had taken place and I started having exceptionally stable blood sugar from my low carb meals. Even the occasional higher carb meal did not result in a diabetic-like BG spike as it once did. Since that all happened (about 10 months into the diet) I've considered myself no longer diabetic. I'm in diabetes remission.

So that's what I remember about the beginning period of adopting the LCHF/keto lifestyle. It really was a healing process with several memorable events along the way. It was hard work to make a break from how I used to eat and make this permanent. I've tweaked my diet some since those early days, but I am still doing it going on 5 years now. I like how I eat. I'm keeping the weight off. Keto works, so I'm sticking with it.

You mentioned missing fruit. I did too in the early months. I limited myself to only a few berries every now and then, but I missed apples, bananas, and grapes just like I did pizza, bread, cookies, and candy. Later I stopped missing fruit, bread, potatoes, etc. They were no longer a temptation. I could take 'em or leave 'em. They weren't part of my new WOE, so I didn't eat them. The funny thing is... While I no longer have any special cravings for fruit, I do eat more fruit these days. I tolerate carbs better. A lot of healing has taken place. I've increased my carb limit over what it was in the beginning. As long as I stay less than 45 net carbs and stick to real food I seem to do OK. As long as it falls within my current carb limit I do allow myself more fruit. I'll sometimes mash a 1/2 banana into a flax muffin. I will eat a grape or two or have a decent size serving of apple slices or cantaloupe. I no longer crave it and now that I can take it or leave it, I can have it and keep things in moderation. That was certainly not the case in those early months. I needed that period of healing to happen first. I still don't eat much fruit these days, but I don't avoid it like the plague like I once did. Occasional fruit, very much in moderation, works for me in my current, slightly higher carb version of LCHF/Keto.