Lots of people here have tried different times. Me? I go for the easy way.
On a normal day I eat as normal (duh!) the following day I eat my 500kcals any old way I fancy. There are diet variations that give you a window but I played around until I found a way that suited me.
I started off not eating until an early tea. I spent the day sipping miso soup and redbush tea. Then something changed and I started eating most of my kcals at lunch, with a teeny tiny supper. Now? Well, I have a salad at lunch and soup for tea, or vice versa
I don't vary my fasting day foods much, a tip from the JUDDD book. Keep it simple and samey to stop you thinking about it. It seems to work for me.
Some days I do fast completely... those days are from about 6 pm through until 6pm. But I have found that I can stretch my 500kcals from 6pm, through the following day, over a second night and on until lunchtime, about 40 hours. JUDDD research says that the 500kcal don't lose you any of the fasting benefits and can allow extended fasting to be done more easily. So, as I want the health benefits as well as the weight loss, this is my usual habit:
DD1: 500kcals from 6pm Sunday until lunch Tuesday
UD1: Lunchtime Tuesday until 6pm Wednesday
DD2: 6pm Wednesday until lunchtime Friday
UD2,3: Lunchtime Friday - 6pm Sunday.
Looks a bit odd, but is is basically Monday and Thursday as Down Days, but as I don't miss breakfast, or I eat at about 10am if I do feel the need, it makes the most of sleeping......
I think that might have been a long winded way of saying, there is no right way, do what suits you best.
Good luck xx