Yes, temperature variations can affect the handling properties, cure rate, and performance of epoxy.
Cold temperatures increase the viscosity of the epoxy, making it harder to dispense (especially via pumps), mix, and apply. Warmer temperatures lower the viscosity so the epoxy can flow more easily through the dispensing pumps, blend more easily to ensure thorough mixing, and flow more smoothly during application, to ensure that the epoxy penetrates porous surfaces to form a strong bond.
In addition to affecting the handling properties, temperature can also affect the cure rate of epoxy. When you mix epoxy resin and hardener, this blending starts a chemical reaction, called an exothermic (heat-producing) reaction. The ambient air temperature affects the temperature of the mixed epoxy, the rate of the exothermic reaction, and the cure time. A warmer ambient air temperature will accelerate the exothermic reaction, and speed up the cure time. Colder temperature will slow down the chemical reaction, and the mixture will take longer to cure. Cold ambient air temperatures can also reduce the chance of having an optimal cure because cold temperatures prevent the chemical reaction from producing enough heat, especially in thinner films. Cold temperatures can also reduce the performance of the epoxy, whether it's used as a coating or an adhesive.
Keep in mind that it's also important to store your epoxy under the proper temperature conditions, as specified by the manufacturer. Keep the caps tightly sealed to avoid moisture contamination, and store containers off the floor and away from windows. The key is to try to avoid repeated cycles of freezing and thawing, which can cause crystallization of the epoxy resin. Crystallization causes the epoxy resin to become cloudy, solid, or chunky. If this happens, don't worry, the resin is still good, you just need to dissolve the crystals and return the resin component to its liquid state by warming it. Place the affected container of resin, with the lid off, in a warm water bath (heated to approximately 140°F). Use a clean stick to stir the resin until the crystals have melted. Remove the container from the water, replace the lid, and make sure it is sealed tightly.