First Batch of Mead

Ok, first batch of mead is in the fermenter, however I think I may have made a boneheaded mistake and added the yeast while it was still too hot, with the likely result of killing the yeast. I thought the cold water already in the fermenter would absorb more heat than it actually did, and I didn't think to check that assumption before dropping the yeast in. Approximately how long should beer yeast take to cause visible fermentation of 8.5 gallons of must? My trial runs took only a day or two to start visible fermentation, but they were significantly smaller amounts of must, and used rapidrise bread yeast which is apparently known for creating larger amounts of carbon dioxide (and lower amounts of alcohol.)