The textbook relaunch runs research, then design, then build, then content, each handing cleanly to the next. Nobody has ever run one.
The reason is not incompetence. It is that each of those phases needs a different person, those people have different calendars, and the plan assumes all four are standing by.
Start from the crossings
Before you write a timeline, find out when each discipline you need actually opens up. Research in three weeks, design in one, front-end in nine — that is not a scheduling inconvenience, it is the shape of your project, and the plan should be built on it rather than against it.
Three things usually fall out of this immediately.
The bottleneck is rarely where you thought. It is almost never design. It is usually the build, or the person who has to write four hundred pages of content.
Some phases can overlap and some cannot. Research overlapping design is fine and often good. Design overlapping build is fine if the designer works in components. Content overlapping anything is fine and should start on day one regardless.
A gap is not always a delay. A four-week gap between design finishing and build starting is a free stakeholder review window, if you plan it as one rather than discovering it.
Book the scarce person first
If one discipline on your project has a long lead time, that is the booking you make first, and everything else arranges around it. This feels backwards — you want to start at the start — but the start is usually the easiest slot to fill.
The classic failure is hiring the researcher immediately because they are free, running the research, and then waiting eleven weeks for a developer while the findings go stale.
Leave the last two weeks empty
Not as contingency in the abstract. As a real, booked, empty fortnight before launch, with the people still under contract.
Every relaunch produces a list of small wrong things in the week it goes live. If nobody is booked, that list takes two months to clear because everyone has moved on to their next engagement. If the fortnight is booked, it takes three days.
This is the single highest-return line in a relaunch budget and it is the first one cut.