Select difference power rates for different times


i want to work out the total price of my power consumption , but i have different rates for different times of the day ie 9pm to 7am , 7am to 9pm etc

i happy to use two different select statements , or if possible change the the maths value (refer selected statement ) i have looks to a solution to include an addition where clause would select data items for a selected time frame
I would like to change the 0.15 below based on the time

SELECT mean(“value”) *0.15/6 FROM “kWh” WHERE “entity_id” = ‘grid_power’ AND “value” < 0 AND $timeFilter GROUP BY time(10m) fill(0)