Yeah it starts at like 3 in the AM and ends at like 9 two days from when it starts. What did you want to know, I can tell you it is tiring and painful but because everyone else is going through it with you, you don't really think about it.
It simulates combat for a short time, though real combat you get more chow and down time. They make it harsh conditions to give you some what the worst aspect of combat though those values are renforced at SOI or MCT. I personnaly like force marches and by the time you start seeing buildings at the end of the crucible your DI will probably start singing cadence which really helped me on the way back. I had a blister the size of a silver dollar on my foot and I think it was starting to get infected, the cadence helped me forget about the pain. I think we only had 3 guys out of the final 66 fell out of the "hump" back so don't sweet the crucible you will be prepaired for it by the time you get to that, You are pretty much good to go if you make it through the first month, unless you get injured or you got absolutly no heart. The training gets harder and your DI's get stricter but you get used to being messed with and your physical capabilities will greatly increase by the time you reach the final 2 weeks of boot camp. You will also get very good at talking about yourself and others in the third person and getting fully dressed in a minute.