Try eating breakfast at 10 am instead of 8(let’s say) for a couple of weeks.
Then see if you can hold off until noon without going to bed later.
If you can eat between the window of noon and 8PM you’re effectively on a 16/8 diet.
After you’re comfortable, try eating no later than 6PM, then try 4PM. Before you know it you’re on a 20/4 schedule.
At least in my experience, the sense of hunger is extremely tuned to one's internal clock. The body seems to absolutely know at what time of day it expects to eat. If I go a long time and never eat before 6 PM, I won't feel even a tinge of hunger until the evening. If I go on vacation, and eat lunch for a week, then the next day I'm ravenous by 12 PM.
The hardest thing about fasting is the transition. Once you've got a pattern, your body seems to pretty much just adjust and it becomes just as normal and effortless as eating breakfast, lunch and dinner. I say that because a lot of people try out fasting for a few days, suffer enormously and decide that the juice isn't worth the squeeze. Whereas I think if you get over the transition hump, most will find it's not nearly as bad as it seems to be when you first start out.
One technique that I think makes for a smooth transition is a modified version of partial fasting. To start, instead of completely abstaining during the fast window, restrict yourself to vegetables and berries. Don't touch the higher caloric density foods like meats, dairy, and starches inside the fast window. Truth be told, this probably isn't that bad a diet just to stay on forever, because it ups vegetable consumption so much. But if your goal is full fasting, it's a good way to make a full transition. Your body's internal clock starts getting used to much lower calories consumption in the fast window, but you don't have to feel like you're starving.
For me at least I go into fasting by first skipping breakfast for a few days, then skipping breakfast and lunch. Skipping dinner is mostly a mental hurdle because there’s so much psychological signaling that you should eat at dinner time and don’t really know what else to do with yourself. Going to bed without eating in a day feels weird at first.
I also make sure to get lots of electrolytes during all of this, magnesium glycinate and lite salt seem to do the trick. Otherwise I start to get shaky and have bad headaches.
The salt and other electrolytes is crucial as you mentioned. If you don't supplement you'll actually get some pretty intense cravings. It was the first time I understood why deer love salt licks. I would have licked on one of those like it was a tootsie pop.
Make sure that you get plenty of water and electrolytes.
Also, if 24 hours is too much, you can try intermittent fasting, and do 16 to 20 hour fasts.
It also seems that some people can't tolerate fasting for whatever reason, so GP might just not be cut out for it.