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I don't think the first day is that important, you have a wet piece of meat the needs to surface dry before it starts to actually dry...thats my opinion , and someone else will chime in to correct me ;)
I don't think it has been quantified...since the weight loss is not the focus at the fermentation stage. Follow a verified recipe and don't worry about the weight loss.
I don't think you should expect any weight loss during the fermentation stage when humidity is around 90%.... IMO, weight loss starts after you move your sausage in the curing chamber where humidity dropped to 55%...