I believe Total Recorder (very inexpensive) (Win only) can be set for timed recording, also the new Sound Forge 7; I've used TR for unattended recording but not the Forge.
http://www.highcriteria.com/
Interesting note (or not): when you click on Help\About in the program, it has an option to go to the "highchiteria" hope page. People don't proof-read squat nowadays.
On the home page you will find something resembling a phonograph in front of a computer monitor.
Yes, TotalRecorder will time the recording, but it is used to capture audio as it feeds to the sound card. It is used for streaming audio and I believe will impose three layers of conversion - ADC, DAC, ADC - to create the WAV file. It does not have an option to terminate on silence, but can be set to eliminate silences; the drawback to that is that quiet spaces between segments of dialogue may be lost due to the inability to set the level of "silence".
Mike mrichter@xxxxxxx http://www.mrichter.com/