Hunger has nothing to do with fat adaptation in my case, the type of hunger is different but hunger itself… That’s all about what and how much I ate previously.
My fasting abilities are way worse than they were on high-carb while not fat adapted (though it was just a very occasional automatic thing) but it’s normal as I had really big meals on high-carb due to carbs not being satiating for me. I needed big meals to get satiated at all but they lasted long. I never had this “getting hungry soon again” until carnivore (breakfast did it too but morning is the worst possible awake time for me to eat, that doesn’t count, I stopped it age ago).
If I want to fast longer, I need a biggish satiating meal. Even for OMAD. It’s super easy with carbs, no way I will get hungry in a day if I make sure I eat as much as I comfortably can for my last meal.
A big meal is easy on keto too but carnivore is tricky… I probably could trigger some OMAD days with eating fat galore, it doesn’t satiate me well but that is useful for OMAD, I can eat a big meal that wise. I just don’t know if it make my satiation long lasting but probably. I should dare to eat really fatty on OMAD… I am not afraid of fat, per se but I definitely don’t eat it galore without care like on high-carb. I have to keep myself back all the time and it’s still not enough.
Did I say I am very determined about OMAD now? I actually will put in some serious efforts. I mean, I will do OMAD and that’s it. I lost patience. Unless I suffer, of course but why would I? OMAD is totally for me. It will solve so many problems. I expect the occasional TMAD day, that’s fine.
Even my better, earlier sleep is helping, 8 hours after my first (and hopefully last) meal I will be already sleeping! And a proper sized OMAD meal always last for that long. Sometimes for 12 hours but then it’s over if I am awake… As far as I can tell, it wasn’t that often that I still was awake at that time, I very rarely eat before 2pm and usually not even then.
So, fasting. I am not a good person to answer as it either happens to me or not… But I know big satiating meal is the key for me. I don’t think fat adaptation changed anything, my woe is more important but especially the size of my meals. But now I don’t get those sharp attention demanding hunger I had before fat adaptation (not always, thankfully, it was very annoying, I just HAD TO EAT ASAP and suffer until then… but often. so when I got fat adaptation and nothing else noticeable from keto, I still was very thankful). Some of my hunger signs don’t urge me to eat, they are adorable. Others are soft but annoying so I eat but I don’t suffer much until I don’t… So soft hunger is great. For a while. Then it MAY pass, that’s cool… If not, I eat as it totally interferes with my focus.
But I rarely have hunger. I get dizziness, weakness and other signs that tells me my body wants food. It’s not an electrolyte problem, I feel I need food (and the passing time is a good hint anyway, my body has its schedule. not a super fixed thing, sometimes I feel the need to eat at 2pm and sometimes not even at 6pm but my perfect satiation usually goes away around 2pm and I can expect urges to eat from that time on).
So. If I really wanted a longer fast, I would wait until I am hungry/ready enough to eat a big, satiating meal. A little willpower or something to wait for long enough (unneeded if I am lucky and my body is fine until late), good planning, good food but part of it is not satiating so I could eat more. Maybe even tiny break before I eat more but the meal must be big.
And then I did everything I could for my meal and should be able to wait a day. And then more… The beginning is the second day is where some hardship may happen but if I am lucky and my last meal was really big and satiating long term, it is doable. If my body is on board, great, I only need to fight with my mind and habits. It’s so ODD to skip a day! Something in me is against that but determination helps.
And the next day my body is a bit far from the idea of eating… But lunchtime decides if I can do more or have to be content with 48 hours. I may get hungry at 45 (it depends when I had my last meal as I get hungry according to the time, mostly. I am an afternoon eater, I was born like this, apparently, it’s not something that changes) but it’s fine, I can wait for 3 mere hours when well-fasted… And busy. And want the number 48 
I did it only once though.
I only did almost 5 days once. Way before I went low-carb. It was very easy and I probably was a bit hungry first, don’t remember but I was VERY curious and had no problems. I surely was well-fed.
And when I reached 3 days or something… It was just normal not to eat. My brain thought about food but my body wanted nothing. Then on the 4th day the complete lack of sodium intake became a fun problem according to my hypothesis 
Cheapest drunk feeling ever, it was interesting and surreal to take my long walks. And on the end of the 5th day I got hungry and ate. A bite. I just couldn’t eat, my body was confused, it desired about no kinds of food but I was hungry a bit… How my body can forget about eating so quickly IDK The next day I could eat normal. Or more normal, it probably still wasn’t my usual huge food intake but I ate normal food.
Sorry, I had a trip down memory lane… Hopefully my mind got all nostalgic and excited and won’t pester me about eating food when I am not hungry at all but I haven’t eaten in the last, like, 26 hours. If I go over that, I probably will reach 40-44 as well. Depends on the time of my last meal. Afternoon eater. Except when it’s night (before bed).
I just hate those 5 meal days (still IF but not good. way too much fat, protein, calories, inconvenience and hunger. possibly carbs too if I get bored of my food).