There isn't any way to maintain the current real time clock when powered down as it is run in the main processor code. Not the low current RTC peripheral. There would be potential ways to do a partial switch-off which reduces power consumption for example by switching off the 5V rail, USB and other functions and reducing CPU clock speed.
That pretty much closes the case :/ thanks, @Hans anyway. BTW is there a way to make it keep the time when powered off but with power supply kept attached??
