Everyone is different with regards to sleep. For most people I think 5 hours is doable but not ideal/healthy. A lot of things will affect how much sleep you need (training volume, stress, lifestyle etc.). If you are going to do this I suggest make sure your diet is clean, stay hydrated, go easy on the caffeine, keep your stress levels down, maybe incorporate some meditation and/or relaxation exercises during the day.
I would also suggest you keep your training volume fairly moderate as recovery may become an issue. Hypnotherapy may also help. A post hypnotic suggestion that you will awaken feeling rested and refreshed after how ever long you sleep can have a real impact. Just remember that what we can adapt to and survive and what is best for us are not always the same, so make sure it's worth the sacrifice.