How long is a piece of string?
It seems to depend on how much other work the GPU is doing at the time. Accessing the Z buffer is heavier than color... and under the right conditions can actually freeze the CPU completely: https://www.youtube.com/watch?v=eFPG70l4Sfc (apologies for terrible quality). No exceptions, machine checks or anything from the CPU; just completely non-responsive upon trying to read a Z value to see if the sun is exposed (for rendering the bloom effect).
It seems to depend on how much other work the GPU is doing at the time. Accessing the Z buffer is heavier than color... and under the right conditions can actually freeze the CPU completely: https://www.youtube.com/watch?v=eFPG70l4Sfc (apologies for terrible quality). No exceptions, machine checks or anything from the CPU; just completely non-responsive upon trying to read a Z value to see if the sun is exposed (for rendering the bloom effect).