@studnavy Okay, I've never tried it on a phone, so for all I know it is only on a PC. But when you're in your chapter, there is a publish button, and when you click it, it will ask if you want to publish now or schedule for later. Click later, and then pick the day and time you want.
I use it for all of my stories, because I can write the book offline, then put all the chapters into draft mode, then set the scheduler to release them on whatever schedule I like. I don't have to worry about anything after that, because they usually happen while I'm just waking up and I wouldn't function well.