I'm confused. Do you mean you fast for 12 hours on each of Monday, Wednesday and Friday, totalling 36 hours? Or you fast for 36 hours starting on Monday, Wednesday and Friday... which would be all of Monday and half of Tuesday etc?
No. It's 36 hours straight of not eating. Think of it like this: You eat dinner at 7 PM, and you go to bed at 11 PM Sunday and wake up at 7 AM. that's 12 hours of not eating. You don't eat anything at all on Monday, and again go to be at 11 PM. You've now fasted 29 hours. You sleep until 7 AM, for a total of 36 hours. You then immediately eat breakfast.
If you sleep for 8 hours and don't snack before bed, you would probably "fast" for 12 hours in a day incidentally
I see, so as an example, you eat your final meal at 6:00 Sunday night. Nothing Monday. Breakfast at 6:00 on Tuesday. 6:00p Sunday to 6:00a Tuesday is 36 hours.