I am a teacher incubating eggs for my 2nd graders. I have a hoverbater that I inherited from the previous teacher. I was given eggs that were left in a car in 30 degree temperatures for a day. When I candled them, only saw blood vessels in 5 out of 18. So I was given another 12 by the farm. My question is they are in same incubator and are 9 days apart. Is it okay to lower heat when it is time for first set to hatch?