The turnaround time will be influenced by many factors, such as
the type of the rendering;
the detail of the scene;
the complexity of the project;
the files you can provide.
To put a number on it, a mid-rise building rendering takes around 2 weeks. Some more complex projects may take a bit longer.
A large condo project with many renderings, amenities and suites can take 6 to 12 weeks to produce.
To save on rendering time, you can reduce the number of revisions by giving detailed plans and specific feedback.