Energy efficiency is one of the most widely used tools for both energy saving and environmental protection against greenhouse gases. Some energy efficiency techniques are being used to reduce energy consumption. This research focuses on optimising the relation of time and energy, where the best scenario of energy-saving for specified applications will be considered with the time required in achieving these scenarios. To implement this, we adopt two engineering applications (car and water pumps) on each application, with specific constraints and parameters to test the time energy relation. It was being found that for both applications, there is an optimum engineering scenario where the least amount of energy (using the extra time to minimise energy consumption) can be achieved while the remaining cases will consume higher energy. For instance, for a specific type of car used in this study, the optimum car speed was found to be between 65–70 km h–1; at this speed, the car consumes the least amount of energy (around 137 MJ when travelling a distance of 100 km). All the speeds less than the optimum speed will consume more energy; the same is true when the speed is increased over the optimum. For the second application using water pumps, it was found that a 1.1 kW pump is the most efficient at pumping a specific amount of water, and using higher or lower rated pumps will consume higher energy levels but correspondingly will reduce the time required to perform the same application. This research emphasised the concept that time can save energy, which is not yet covered in the literature as time value of energy when time is not an essential aspect and can be delayed without affecting the main tasks.