A dishwasher would likely be safe left on overnight.
However it's not recommended to leave your dishwasher on overnight unattended because it could potentially cause a fire or even cause a flood.
I once left the house with the dishwasher on and came back a few hours later and the kitchen was flooded with water because the dishwasher got clogged up and the water float switch would not shut the water off.
So I would not leave the dishwasher on unless I was awake and able to check it out every 30 minutes or so.
It's not worth the risk.
Just run the dishwasher an hour or so before bed and then turn it off.
Then you can unload the dishes the next morning.