I am not sure if OP is trying to devise a training program for an ultra race or 1200k. I also don't know what the best preparation would be for either. I know what it feels like to me, you do a pretty hard 300k or 400k and feel like you could do another. Driving home after the event is literally no big deal. You do not need much of a rest day. I wish I knew how to get a magic training program. I do think volume (miles and hours) matter more than fancy smancy zone this and zone that structured boring training programs.