Water comes out of the ground at approximately 56°. After the electric is connected, fill the spa placing the hose into the filter stem pipe that will take water directly to the pump to prevent an air lock. Fill it to above the jets below the pillows and then power up the spa. Depending on where you live, the water will range from 48° to 56°. DO NOT FILL WITH HOT WATER.
Think thermal, if it is 25° out, the shell is close to that temperature. Initially filling with hot water can cause damage, as the water can be near 140°, and the cold plastic will not like that. Acrylic and plastic components react to thermal differences. Once the spa is filled to above the seats, you can resort to hot water if you feel so inclined, other wise 220v systems will produce 8° to 10° per hour. No need to be in a hurry.
Moving water will not freeze, but standing water will. IF and when that occurs use a small space heater inside the EQ area to prevent ice from forming, or thawing the ice that has formed. Starting a pump that has been frozen can be bad news. When you power it up, the torque can twist the iimpellar right off the shaft as the impellar is frozen in ice.
You should have no problems, but they include the "disclaimer" just to say, it not their fault.