*shrug* - the manual doesn't say to give the device a break every 15 hours. Simple as that
I'm just curious, do you turn off your router at night? Physically turn your games console off? It's the same thing - if the manufacturers thought we'd get better life out of their devices by "giving them a rest" it'd be printed clear as daylight over all the packaging. Then, if something broke because we'd left it on too long, what a way to void our warranties!