In a track race everyone has the same finish line.
In real life we have different finish lines all the time.
When building a house, you want the plumbers to finish before the drywallers begin.
When selling a software program the coders need to have most of their work finished before the sales and business development people start on their end.
Managing different finish lines (and different starting lines) is an important part of project management. The first step is simply to figure out how long everything will take and then figure out what has to be done (or what stage has to be done) before the next one can start. Then, and only then, can you establish the true time line.
Have a great day!