fjfj7654 you can set times in dnd settings on android to auto have it turn on at certain times easily without any apps.
As for grayscale I can't find an app but there probably is an open source automation app that might have that be able to turn on at certain time every night.
But I would actually say for greyscale use the quick setting and instead use auto nightmode every night. It will make your phones blue light less and help you sleep. But also it will make your screen yellowish or orangeish so you probably won't wanna watch stuff and be on your phone because it will look ugly the colors. But it will help you sleep.