First, check your curling iron's user manual. The optimal time can vary based on the material on the curling iron. Then, start with 5-6 seconds on a few sections and check the results. If the curls look like you want, then you're good. If they're falling apart quickly, hold for a few more seconds.
If you need a quick hairstyle without waiting for each section of your hair to curl, try these five-minute hairstyles.