That depends on a lot of factors - how much you have to lose, how close to your goal, activity level, etc. The answer is going to be somewhere in the middle most of the time.
Shoving all their calories into one window gives most folks a lot of flexibility on food choices, but that doesn’t mean they can get away with completely unrestricted eating either. It’s certainly possible to eat at or above maintenance in one sitting. Another aspect to consider is you’re also trying to get all your nutrition for the day in one go, not just calories.
My two cents, have some things you enjoy from time to time, but work on getting into a better relationship with food as well.
You can, technically, but having given myself scurvy before on a bad died of fries and soda, Id highly recommend making sure you’re making more of your meals balanced than bad. If you don’t improve your relationship with food and making food choices, then you’ll be the exact same place.
Honestly I found omad to be a smooth transition from 18/6. You’re already used to not eating for extended periods of time, I found it easy to just push that window. Personally, I found when I was fasting after hour 20 you’re not even hungry anymore so it’s easy to go to 23 hours. Good luck