I would have thought that it would be advisable even essential, to run the heat pump on the night rate, which is 50% the cost of daytimeunits. My heatpump is rated at 3kW and runs at night, building up the heat in the floors ( my current bill is €160 for 2 months for heating). Whether you need to run it for top up during the day for a short period will depend on many things, such as the build/insulation standards etc.
Apart from heat pump hight saver can be used for many other things such as dish washer, clothes washer and drier, or domestic hot water heating.