It depends on your flow! The styles with a 4 or 5 tampons' worth of absorbency were designed to last all day or overnight even on heavy days for most women. But if your flow is extra-heavy, you may need to have to change them once. After you develop some experience with them, you should be able to feel when they start being full and need a change. They will wick moisture less quickly and start feeling damp. That should be your cue to change them! But you can definitely wear them for as long as you feel comfortable, even overnight. We do not recommend wearing them for more than 12 hours for hygienic reasons.