on the my cloud home a 40 sec reset should only demote the device owner. to erase data you need to use the 60 sec reset.
when erasing large amounts of data it will take a while but 75 hours seems a bit excessive. Is the LED fast blinking or slow blinking? there could be different things going on depending on the LED behavior. It looks like a system erase will not occur if there is no active internet connection and if the LED is blinking fast that means there is no active internet connection.
here are some knowledge base articles i found for resets
