Once braces are off, how quickly do teeth settle?

3 to 6 months: you need to wear retainers to hold everything in place otherwise the movements will reverse. Teeth are held in place by a balance of forces, the pressure of the tongure pushing out and the lips and cheeks pushing in. They lie in the neutral zone. The collagen fibres holding the teeth in place are replaced very slowly, with a half life of six months. 18 months for them all.

They begin moving immediately, and will continue to do so throughout your life, Want to prevent untoward movement? Go looking for reasons too put your retainers in rather than excuses to take them out.