In theory there is no limit but it would be good to see noticable effort put in. Taking breaks is encouraged if you know you'll need a long time, if you plan them to be between games then you can have a more representative time on the IGT timing, as long as your run stays retimable. I personally wouldn't attempt sleepless anyway until you're sure you can go below 40 hours. A rough blind estimate (not factoring in breaks) is about 80 hours, if you can beat that the time will certainly not be viewed as too slow if anyone decides to complain for whatever reason.
You can now submit runs to the 602 and 1862 leaderboards under the TA filter if you took breaks for sleep and paused the timer! Rules will be more in depth on the category pages on the leaderboard.