You don't want to do the rehydration the night before. The yeast should only be without food for 20-30 minutes, otherwise they begin to starve and begin the process of going back into dormancy.
I know this is an old thread, but I have an experience to add.
I have made 10 x 5 gallon batches of apple cider all using half a packet of Kitzinger Reinhefe Champagner (dry champagne yeast). With 9 batches, I rehydrated for 2-3 hours each time (simply because I'm lazy and just get back to it when I get back to it). All 9 of those batches showed lacing at 12 hours and started building up the krausen after about 24 hours, and all 9 of those batches finished in a week or so and tasted fantastic a day after cold crashing.
So, the 10th batch just got started. I put half a packet of Kitzinger in a glass of water and put a plastic bag around it like I always do. And then I forgot about it until 26 hours later. So, after I had remembered that it was still there then I poured the juice, sugar, and 26 hour rehydrated yeast into my demijohn. This time, I had a full kreusen in 8 hours instead of the usuall 24. I'll let you know how it tastes.
I don't measure the water temperature when I rehydrate my yeast, I just feel it with my elbow and pour in approximately half a packet. I don't even use a sanitized glass to rehydrate in, just one that has come out of my cabinet shelf where the rest of my glasses are. They all get dishwashed regularly enough, having 5 people in the house.
I found half a packet of dry yeast that had been in my fridge for over a month, used that one and it worked just as well as the others. It wasn't sealed or anything, just folded in half.
My point is that, even given my lackadaisical approach, it seems to be exceedingly difficult to screw up a fermentation. Either that, or Kitzinger Reinhefe is a far more hardy strain than most anything else on the market - but I don't really believe that.