I am not sure whether this is helpful but you can try.
In .adds\kbmenu\log\uptime.txt you will find something like
Code:
powering off at: 2015:07:027_12:53:47, after 0:00:03:53 uptime
The log file is only written when you power off the device, not when you only reboot it. If you want the log file to accumulate the information, instead of containing only the most recent, replace in .adds\kbmenu\onstart\poweroff.sh
by
If you want to read the log file from KSM, select:
scripts > browse > browse kbmenu.msh > log > uptime.txt
If you want to see the current uptime, select:
scripts > tests > returntests.msh > show uptime.sh