Each soy wax melt is designed to provide ~12 hours of scent. As the wax melt gets closer to the 12 hour mark, you'll notice the scent to weaken. This is when it's due to be replaced.The performance of any wax melt is dependent on the way the wax melt is heated. Too hot and the wax melt will burn off the fragrance too quickly, resulting in a very short, strong scent, likely progressing to the unwanted smell of burning wax. This is often caused by either a large tealight (8 hour or deep 4 hour tealight) or a short wax melt burner (less than ~9cm in depth). For the wax melt to last for the advised time of ~12 hours, always use a small, 4 hour tealight and a wax melt burner between ~10 and ~13cm tall. This will maintain an even heat throughout.