You can make the depth anything you want. To make the inlay fit snug, you need a gap above & below.
But the dimensions are all up to you, and can change from job to job. If you have a thinner stock, or an inlay with small details. the dimensions will be smaller.
Once you understand the concept, it’s pretty easy to make the adjustments to the sizes.
The Fenrus tutorial that Julien linked to, particularly post 5 (Using "Advanced VCarve" in Carbide Create 461 to make Inlays - #5 by fenrus) will help you understand the concept.