You are really asking two questions. I can give you my experience with this.
I have my wireless charger in my bedroom. If I happen to go in there and I have my phone on me I will put it on the charger. I have not had anything bad happen from doing this.
I also put my phone on the wireless charger all night. I basically use it as a bedside clock and alarm clock. Nothing bad has happened that I can see.
Good luck with your phone.