Generally, a medium size custom kitchen design takes about three months from project start to completion. As the design stage can take longer, I’d recommend this to be the minimum amount of time you allow between when you contact the kitchen designer, and when you want the new kitchen to be installed and functional. The kitchen or bath design stage can take two to four weeks, depending on size and complexity. It’s always best to allow as much time as possible. I’d recommend contacting the kitchen designer before final blueprint stage (for a new build), or before commencing on any work (for a renovation).
Not that we haven’t helped on projects that are further along, but it can possibly limit your available options, or cause unnecessary delays and expenses.