It depends a lot on the CAM module and if your channels are encrypted. I have irdeto and viaacess, and the irdeto is very slow (up to 15 secs) for encrypted channels. The viaacess is however faster (a couple of seconds).
I recently got a new irdeto, and that is very slow compared to the previous one.
For unencrypted channels both are usually fast (1-2 seconds)