Is it hard on a heat pump to use alternate heat source (kerosine heater,other) causing the heat pump to be off for long periods during the day and than allowing the unit to come on at night?

Is OK to use a supplemental heat source with a heat pump; i.e. a kerosine heater?

It is not any harder than if you just turned the unit off. Usually a heat pump has a bit better performance during the day because the outdoor temperature is higher during the day.

Example

If you use your supplemental heat during the day and you turn your heat pump on at night the heat pump might not be able to maintain the temperature in the home so the electric resistance heat might come on to make up the difference costing you additional expense. Now these resistance heaters will come on at night no matter what other source of heat you use during the day but the ideal use of supplemental heat would be to use it at night. Naturally most people do not use a kero heater at night while they sleep due to safety reasons but this was just to give you an idea of how upside down the situation is with heating.