There are plenty of people on the forums who have reported that a 2nd non-display card in windows doesn’t have the 5s watchdog timer with CUDA 1.1.
There are also a number who have mentioned that they were having problems with it. I don’t recall the post, but I think someone from NVIDIA said that a driver bug was causing 5s timeouts on non-display devices in windows in the CUDA 2.0 beta.