Audacity always records everything at 32 bit depth, so recording overnight is going to use ~500Mb/~0.5Gb, (mono, not stereo).
A voice-recorder will run +8 hours on a fresh battery. You can then download the recording into Audacity.
Such recorders can be set to run at 16bit 22050Hz which is good enough to record speech. The overnight file will be ~125Mb which will only take a couple of minutes to download via the USB.
If you are going to log the times of events you may find these Audacity plugins useful … Labels to show time that a recording was made