When should concrete forms be removed?

It depends. If the air and ground are warm, it might only be 2 or 3 hours before the forms are stripped. If a high-early-strength admixture is in the concrete mix, the forms could likely be remove at around an hour after placing it. This could result in stress cracks in the placed concrete, however.

On the other hand, forms hold water inside the concrete where it is critically needed for the mix to cure and harden. If forms are stripped in the first 3 days or so since placing the concrete mix, then other means must be used to keep the water in the mix. A spray coat of latex liquid (Curing compound) can do it. A sprinkler running 24 hours per day can do it (This is the best way), or a covering of plastic sheeting can do it. Some people still use large burlap blankets soaked in water to cover the concrete.