Very few projects come in these days with any sort of lead time. Most of my clients want the masters back within a few days at most.
My theory is that the old model of releasing music, through established labels that had a good understanding of the logistics of each phase, has changed dramatically in the last ten years. These days, artists are often the ones releasing the music themselves or are working for Internet labels that are new and have no physical merchandise. Everything can happen "instantly" from the inception of the music, to the promotion via social media, to the release via Bandcamp. Twenty years ago, it was in everyones best interest to generate enough publicity before the actual release, to ensure the label would be able to unload all of the physical merchandise. So it meant taking out ads in magazines, sending out promos, and giving the distributor a release date. This gave the mastering engineer a nice buffer of time to work with. When you're promoting your label on Facebook, and selling Mp3's on Bandcamp, there's not a lot of risk.
Just my two cents.