I often violate that rule, riding too many miles on day 1. Last year in MT my first day turned out to be 90+ miles when the smoke had cleared. (I'll advised, impromptu detour from the planned route added miles.) Two years ago it was about 82. I need to get away from that. Three years ago it was about 85. 2015 also featured a hard first day than a very had second day. I was knackered.