The heating time for a lava lamp can vary depending on the size and model of the lamp. In general, it can take anywhere from 1 to 3 hours for a lava lamp to fully heat up and start working properly. During this time, the lamp's wax and liquid will gradually heat up, and once they reach a certain temperature, the wax will start to rise and fall in the liquid, creating the characteristic "lava lamp" effect. It's important to note that some lava lamps may take longer to heat up, especially if they are very large or if they are located in a cooler room.