Officer has to lead so he has to be better then his men...well thats the theory, they have to do the 30 miler on their own too and navigate it don't they?...lonely
37 weeks is the initial phase but as it is a common happening, most people get back trooped for some reason so say 40 weeks to round it off, then after that there is more tests and officers are generally tested and marked alot more rigorously then general duty marines because of the field of work they are applying for.
Besides that don't let it put you off, if you think you have the POTENTIAL go for it.