I wonder if there is a way to get the time that the device has been running since the last reboot?
From: http://developer.android.com/reference/android/os/SystemClock.html
elapsedRealtime () and elapsedRealtimeNanos () return the time from the moment the system boots and turn on deep sleep. This watch guarantees monotony and continues to go blank even when the CPU is in power saving modes, so it is recommended that you observe the general time intervals.
In response to this other question :
Go to Settings > About Phone > Status and scroll to the end. You will see the waiting time.
Settings
About Phone
Status