The total rendering time is affected by the number and complexity of shaders. The amount of calculations required by individual shaders can vary greatly. In general, volume shaders are very time consuming whereas surface shaders are quick.
For more information about shaders, see The Shader Library and Working with Surface Shaders [Materials and Shaders].
Experiment with different shaders to see whether you can get a similar effect that renders more quickly. When rendering, you can activate only those shaders that you require for the current render pass on the Active Effects tab of the Render Options property editor.
If you don't need transparency, reflection, or photon effects, try using simple material shaders (such as simple Phong or simple Lambert).
If you only need one raytracing parameter, transparency for example, from a complex material shader, use a simple shader instead and attach a transparency node to it.
To speed up rendering, deactivate any unused parameters in complex material shaders (like Phong or Blinn).
