Pretty sure not too long ago Vimm asked for people to not do this. If you want to do it I can't exactly stop you, but it's not a feature on the website.
"NintenDON'T sue me please haha"
I would also like to know if there is a way to do this? Best I have found is a program called Free Download manager and the ability to schedule download times but you can only do this hourly and exactly on the hour and even then you have to guess how long a file will take.