Thats an interesting bet, considering I am absolutely positive I could do that if I were currently traveling, even starting today. I think the reasonable limit is about 7 days real time though, even playing hard core (which I would have to do). Although, for best results, I would pick a tankable class and level him as such through the LFG tool.
On a dare, I leveled a Tauren warrior on a new server, so had no advantage of any gold or heirloom items. This only took about 4 to 5 days 'played' but took place over a few months so part of that was using rest XP. I leveled Mining, BS, first aid, cooking, and fishing along the way though, so I could have done it in less time.
Given leveling ONLY, with gold and heirlooms, 20% reduced Xp required 70-80, but no rest time, four days 'Played' is still reasonable.