Who the hell has a conversation for 24 days ?!
Could be conference meetings. I've seen conferences that ran 24 hours a day for half a week before. Security surveillance/audit is another. While conversations sort of throw it off, doing soundscapes of an area over long periods of time (like looking for a certain call/response from a critter) would be another situation where long record times are needed.
anyway, besides the point, if the requirement is that you be able to record continuously (and unmonitored) for upwards of 7 days, I can think of 2 solutions:
- a laptop with a USB interface
- a 7 series with upgraded hard drive or jumbo external firewire drive.
The problem isn't necessarily quality, but size of the resulting recording. This could be compensated by running at 16 bit, but then you would need to have better control of the levels which if unattended could be problematic. In both instances I'd run a limiter and long (balanced) XLR cables so you can stash the recorder/setup in a safe place and run the mics from other locations.
You'll do better (read: cheaper) with the usb interface if you already have a PC you are willing to use. An older usbpre1.5 or similar box can be had for around $400 or so, others maybe more or less.