I'm having trouble understanding your request. You want a definitive number for up or down states for a range of time (for example last Monday thru Friday)? What state would you report for a device that was down for 5 minutes on Monday? Would that state be different from a device that was down all Tuesday? How about a device that was down Wed thru Friday? How do you factor in lack of update due to busy controller (meaning controller either didn't respond to polling or had a delayed polling response)? The report answers these questions by giving percentages of up or downtime for the range with a few options to distinguish communication errors from reboots. In the weeklong report, what's the threshold that determines if a device was ultimately up vs down for the reporting number? Is it any downtime / 50% downtime / 100% downtime = down device? What about missed polls? Devices marked down due to missed polls might bring about false positives.
Most customers are only concerned about downtime for troubleshooting. These customers use the 'planned maintenance mode' setting on device's manage page to exclude devices from being reported as down during known windows.
Perhaps you're looking for a trending graph instead? If so, you could create a script to pull the up/down state from the ap_list.xml. The is_up state in ap_list.xml gives the up/down state from the most recent polling interval. Rate of collection from the script should match the polling for up/down state on Group -> Basic page (default 5min, min 15sec, max 30min - if the system resources allow as polling cycle rate is directly proportionate to number of devices that need to be polled and the CPU/Memory capabilities of the system).
It could be that we are discussing a possible feature request to enhance the report, which would need a better understanding of how you view the numbers and what usage you take from them.