How many hours of audio will fit on a CD for transcription?

I'm expecting a CD with audio files to be transcribed. The client has not specified the amount of audio hours on the CD and he is unavailable to contact for the next couple of weeks. Because of the postal strike in Canada, the CD has not arrived and I have no idea how much longer I have to wait and I have other clients waiting. Any idea how many audio hours will fit on a CD? Any help would be appreciated. Thanks