So what’s the answer? Most Nikon cameras have the option of an automatic cleaning cycle, which can go a long way towards ...

The Nikon D3100's startup ... startup and shutdown by default. (Sensor cleaning is preempted by the shutter release, and likely continues briefly after the camera is shut off.) ...

Enabling sensor cleaning increases shutdown to 2.2 seconds ... That small an increase is excellent. Letting the camera choose the autofocus point increases full AF shutter lag to 0.351 second.