That's true. Generally at least 24 hours. Of course you'll still have the pump running to mix it all. Once you feel confident you're showing good salt readings and turn it on, you'll find yourself testing and adjusting back & forth until you find what works for your pool based on size, equipment output, direct sunlight, etc.
Since you have new water, watch your FC level (keep some bleach available as a back-up) and ensure you have CYA started for that minimal target of 70 ppm.