The reason that it's sometimes better to run your dishwasher at night is that in some places and with some electric utilities they will provide a cheaper rate for your electricity at night when there's lower demand for the electricity.
Not all electricity utility companies lower your rates at night though so you might not save anything running your dishwasher at night vs during the day.
Where I used to live we would get cheaper per kwh electric rates from the utility in the evening hours and during the night so it was a bit cheaper for me to wait and run my washing machine as well as my dishwasher and dryer during the night.
However I never went to sleep with either on and just washed the dishes and washed and dried the clothes during the evening and by the time I got to bed it was all done with.
Check with your local utility company to see whether you get cheaper electric rates or not because sometimes you do and sometimes you do not.
Where I live now the electric cost is the same cost in the day and at night.