What are is the growth rate of bacteria measured using a ***** culture that has been incubated for ~16hrs?

Why not at 12 hrs, or 24 hrs, 48 hrs etc. Does the growth rates reach a maximum at 16 hrs?

What are is the growth rate of bacteria measured using a ***** culture that has been incubated for ~16hrs?
Usually at this point the culture is well established, and dilutions will then be made and the optical density of the dilutions can be figured out, which determines the growth rate. After 24 hours cells start to die off b/c of lack of nutrients. After 48 hours, the culture will still be viable but not the best source of robust growth. 16 hours is pretty arbitrary I guess, but it usually represents an overnight incubation, ie incubate at 5pm, come back at 9am.