Depending on how fast you count, it's about an 8 count. Once you get the feel for it, you'll know when the jig should still be falling and it's not. Then you'll know to set the hook! When in doubt, set the hook. If you see the line twitch or "act different" set the hook. A big help in jig fishing is using high vis line. You'll be surprised at how many unnoticed bites you get when you're not paying attention. I've tried to teach this to many of my friends. Some get it some struggle. Good luck!

Chris