||04-25-2013 08:23 AM
Most DDs last about 36 hours. If, for example, Sunday is your UD, you eat your last meal (I'm assuming) somewhere around 6-7pm. When you eat your last, that's when the DD officially starts. So through the rest of that evening, while you sleep, all of Monday and then while you sleep Monday night, you're on your DD. When you wake up Tuesday morning and start eating again on your Tuesday UD, your Monday DD is over. So for most people, depending on when they stop eating Sunday night and start eating Tuesday morning, their DD lasts somewhere between 30-45 hours.
There are a couple threads about when to break your fast that talk more about this. I'd suggest reading through the stickies, and go back 4-5 pages of threads. This is a really busy board, so threads with important info get buried fast. Read through the monthly newbie threads too, many of the newbie questions are similar and there are great answers in there that can't always be reproduced.