The model and size of the hot water heater determine how long it takes for the heater to warm up. It may take more than an hour for the water to warm up completely.
A gas water heater may be able to refill its supply of water in an hour, while a similar electric model may take more time. Tankless water heaters only heat water while it is needed, so it seems like it is faster and more efficient. A water heater only holds so much water, so choose a size that is correct for the home it will be in. A larger family will need a larger water heater.