iPod Nano 5g recording specs?
Apple's information article on recording on the iPod nano is here.

The iPod nano can operate for up to 24 hours on a battery charge.

The built-in microphone is monaural and, I guarantee you, is of the lowest quality. You may be able to purchase a compatible third-party external monaural microphone of higher quality that connects through the headphone port or the dock connector. Consult the microphone or headset manufacturer for compatibility information for the iPod nano.

Apple does not state any restriction on the length of the recording. The document I cite above states that the iPod nano records in WAV format, which usually implies 16-bit 44.1KHz uncompressed audio, and in this case it will be monaural using the built-in microphone. This kind of file takes up 5MB per minute in file size, and I assume that you can continue recording until the iPod nano's battery runs down or until the iPod nano no longer has any available file space to hold the recording.