Substrate and heating

I'm currently in the process of improving my leo's tank and I'm not sure what to do for heating. I've read that overhead lighting is best but does that mean I should get rid of my heat mat when I switch to an actual substrate? Or can I leave the mat and just put the substrate over it? Also, if I take out the heat mat, is it safe for my gecko to go all night without heat since my house is normally around 72° all day.