Well that really depends on the time you have available for preproduction. For example, if this is a short film and you have about two months of preproduction, I would audition at about the one month mark. This gives you enough time to plan out what kind of people you need and also still leaves enough time for call-backs, offers, and time for actors to meet, memorize, and prep.
Of course, if it's a larger scale full-length. You'll need more time. Maybe then, audition 3 months out from shooting.