Biscuits and Gravy can safely sit out at room temperature for a period of 2 hours.
After 2 hours the gravy and biscuits will start growing bacteria that could make you sick so if you've left biscuits and gravy out with the biscuits covered in the gravy then it probably should be thrown out.
However if the biscuits had no gravy on them the biscuits should be still okay although they might be hard after sitting out.
But the gravy may not be good to eat especially if it has any meat in it.
If the gravy contained no meat and it still smelled okay after 2 hours then you could refrigerate it and possibly eat it.
The worse that will happen is you get a stomach ache or a non serious food poisoning.
If in doubt though just throw it out after it's been out 2 hours to make sure you or your family doesn't get sick.