I've been IF'ing regularly for just shy of a year now -- my normal, workweek approach is to simply skip breakfast and push lunch until after my midday workout, say 2 or 3 in the afternoon. Then I eat dinner around 8 or so. I do tend to have a large handful of nuts when I get home from work, around 5:30/6.
So roughly a 15-18-hour fast around 5 days a week. Weekends I tend to eat three meals, but one is quite small. Every few weeks I'll also throw in a fast of 24+ hours, up to 40-48 if I feel like it.
I'll also have days where I just eat dinner plus the get-home-from-work snack, so more like a 20-hour fast.
But I worked up by skipping breakfasts, and pushing my first meal slowly forward to around 1:00 after an 8:00PM dinner. Took about a month to get used to it. Now I just mix it up however, based on how my body feels, which is a seriously nice feeling. Busy? No time to eat? No problem! Feel hungry? Good food around? Chow down! No problem!
It's *awesome* once it's dialed in.