The warmer temp will just make them hatch faster -- say 24 hours. How will you use a heater? You might try a 100 watt incandescent light bulb in a fixture about 6-10 inches from the hatching bottle (remember mine are thick milk jar glass and not meltable plastic!!!!!) to raise the temp. or place the bottles themselves in a half filled 10 gallon tank with a small wattage submergible heater in the tank itself and heat the tank water so that it then warms the hatching bottles' water. Glad it's working. Shrimp is easy once you have a teacher. I had a great teacher.