You will only be able to collect up to ~14 hours of data (limited to a maximum of 100 million samples per channel).
If you require a longer period of data logging, you can use the Software Development Kit to create your own application to capture and log data. You can use aggregation to obtain only the minimum and maximum values for every block of consecutive samples.
The Software Development Kit is available on the supplied PicoScope installer CD (look for the PS4000SDK... folder) or alternatively you can download it from our Software Downloads page:http://www.picotech.com/software.html
I hope this helps.