NOTICE :
The mold is reusable. You can clean it by spraying them with garden hose.
The molds can be used again right after you pour the first garden stepping stone so you do not have to wait.(Don't wait it 100% dry, or it will be really hard to remove it.)
The thick level of concrete can be varying depends on your requirement of garden stepping stones. A wetter mix of concrete for concrete molds is used to get garden stepping stones with ground / lower level, and a stiffer mix of concrete is used to get garden stepping stones with higher / stone level.