Back on topic, the opening post asks could more have been done to preserve a potential crime scene and in my opinion it couldn't. One has to put oneself in the shoes of those first two officers who attended and whom according to some were inexperienced in such events. Children go missing every day in every part of the world but most are found quite soon afterwards, the two officers who initially attended Ocean Club that night will have come across many such incidents of missing children so did not rush to the scene. They probably thought to themselves that she would turn up before they even got there and it was only because of further contact from their commander that they then decided to rush to the scene.
Their first priority is to gather information before setting up further searches around the perimeter and further afield. The only evidence of anything untoward was the claim of a raised shutter and an open window which the two officers undoubtedly attributed to the missing child. Gerry McCann had himself opened and closed the shutter so I am not in the least surprised that the GNR didn't immediately think 'crime scene'. One has to remember that the officers never saw this missing child, they knew she was almost 4 so they would have thought it very possible that she had opened the window and raised the shutter before going outside by either the window or the unlocked front door.
It was only later (nearly an hour later) when the watch commander arrived on the scene that it was decided that something sinister might have gone on and so it was decided to protect what was left of the potential crime scene.
I don't believe they could have done any better in the circumstances.