In general concrete (not sure about pool specific stuff) should be kept wet for several days after it is poured or should be painted with sealer to lock in moisture so it can cure correctly within 24 hours of being poured. This can be done a number of ways, through the use of wet burlap, running lawn type water sprinklers on timers every X hours, covering in plastic, etc. Failure to seal or keep freshly poured concrete wet for the first week or so after it is poured tends to lead to surface cracking.