sexual practices require foundational practices to be achieved first. if you rush through the foundational exercises without learning them properly and giving them their requisite time because you want to achieve a non ejaculatory orgasm, then you will never get there and will likely hurt yourself in the process.
100 days is generally the time it takes to completely fill the resivoir, basically the time it takes for your body to 'switch gears,' as it were, to where the body is beginning to put less emphasis on generation of fluid and using your core energy elsewhere. building the root will happen more quickly and efficiently with 100 days. it wont completely destroy your practice if you dont, but it does slow your progress.
check out
www.alchemicaltaoism.com and there are some good links with respect to this subject, also some good words of caution.