It works. But not for the reasons you think.
There is no magic to intermittent fasting. No re-balancing hormones, giving the body time to detox, going into ketosis (it takes between 2-4 days to be in ketosis) or fat burning zones. It simply makes it harder to consume calories.
It's all about timing
The most common length of a fast is 16h from 8pm-12pm. So that’s an 8h window starting at lunchtime for feeding.
The reason this is the most common window is that it gets results. How does it do that if it's not doing all the magic I said above? It simply stops you snacking after dinner and most importantly stops you eating breakfast. If you think about it, most of the fasting happens while you are asleep, when you wouldn't be eating anyway.
For the most effective fast, it should take place during the most obtrusive hours, BUT it needs to be easy enough to stick to. If the conditions of a diet are too harsh then medium/long term adherence decreases massively over time.
Recommendations for faster results
I recommend moving the fast to start and finish 1h later if morning and lunchtimes are the main issue or one hour earlier in the evening if snacking after dinner is the issue or their social life leads them further from their goals.
To get through the longer fast in the mornings it is perfectly acceptable to have a black coffee or 2 with sweetener as they are less than 10kcals each and if you are having that compared to a full breakfast and a mid-morning snack/calorific coffee you will still be reducing your calories massively.
Still log your calories throughout your intermittent fasting and you can see a big dip when you start. As long as you don’t see the feeding time as an “I must get as much in as possible while I can” time, you can expect to lose weight quite quickly.