An outsider can wonder why, we must spend all the time and effort for curing concrete , when we apply water or hold it wet with blankets for long periods even after concrete hardens.

The answer is a process called "hydration"

Cement needs to fully hydrate in order to make enough bond between sand aggregate and steel in the concrete. Cement hydration is what gives the concrete its strength. For this cement needs water.

The official design criteria for curing period is 28 days but in general due to scheduling needs, shorter periods are possible if necessary precautions are taken. So for example a 4000 psi concrete means, the concrete is designed to reach 4000 psi in 28 days ASSUMING it had proper curing. Earlier than that, it will be less than 4000.

A concrete which is not cured will break and fail. Proper curing is a MUST. Plan your schedules and costs and site accordingly.