vectra ccr600 code input after "7safe"?

I've been advised that the ignition has to be left on for a "lenght of time" to get the "enter code" read out after "7safe" comes up. Any idea how long and should the radio be on or off during this time? I do have the codes for both cd changer and radio. Thanks in anticipation. MAX. IF i get it sorted b4 i get a reply i'll post answer anyway as it may help any others with same problem.