[dnanian]

The issue here is that the SD! application sleeps the Mac after a few second delay, but the drives are ejected by the 'schedule driver', which might take a bit more than that to get control back. So... you could have your Mac simply time out normally (and go to sleep)... since I don't know whether forcing it to sleep at 3:30 is a good idea: it's hard to know when the backup will really be done.