Something you may wish to do right at the very beginning of your process, is set a release date. This may provide you with the motivation to get tracks done, and to push forward with promotion and suchlike, but there are a few thing to bear in mind.
If you intend to use a PR company, they prefer to have at least 4 weeks to work their magic, and more often work better with 6 weeks or more to run a promotional campaign. You may also want at least a month to do your own promo and chase up any contacts about coverage.
If you are pressing physical items, this will be your big time-consumer, since vinyl pressing can take up to three or four months (at busy times) and will almost certainly take at least 8-10 weeks.
Luckily, digital has no manufacturing time, however if you are using a distribution company, they may require a 4-week lead time, in order to be able to set up the release on all relevant stored in time, and if you use a self-managed option, you may want to allow a week or so, for the site to propagate to stores (all of them should also allow you to set a future release date).
So, with mastering and artwork times, times for promotion and time for distribution, often you should give yourself at least 6 weeks to release your music – but generally aim for 8-12 weeks (or more).
[I provide a customisable schedule template document in my *How To Start Your Own Record Label* course]