This page gives information on the Render Time Render Element.
The Render Time Render Element shows a floating-point number for each pixel's render time measured in milliseconds. The colors in the render element show the rendering speed as a range from black to white. The whiter the pixel, the longer the render time and vice verse. This render element works only with the Bucket image sampler. The Render Time Render Element is useful mainly for troubleshooting purposes.
This render element is enabled through the Render Elements tab of the Render Setup window in 3ds Max and displays its parameters in a rollout at the bottom of the window:
VRayVFB – When enabled, the render element appears in the V-Ray Virtual Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.
Example: Per Pixel Render Time Information
Hover the mouse over the image to see render time in milliseconds information about any pixel.
The information is visible in the bottom of the VFB (right next to the Raw option).