No, SPF 50 does not mean you can be in the Sun for 50 times longer than if you weren’t wearing sunscreen

The higher the SPF rating, the more protection provided. But the number indicates a different value than many people think. “SPF does not tell you how long you can be in the Sun without getting sunburn,” the US Food and Drug Administration (FDA) notes. “SPF does not mean that if you normally burn in one hour and you apply an SPF eight sunscreen, it will take eight hours for you to burn.”