Doing well on CS doesn't take a ton of studying but it does require an ability to perform a strong, focused H&P, come up with a reasonable differential, and construct a solid progress note. Many people take it in the Spring if they've completed most of their core rotations. Things like medicine, family, and peds give you good experience so it's probably best to have them done before you tackle Step 2 CS.
There's no real rush to take it though, unless you're just looking to get it out of the way. Once you have all your core rotations behind you it shouldn't take more than a weekend to prepare. Make sure to schedule early though, because slots fill up fast.
