What are the parameters for the type of sand to be used in the sand timer? Does it have to be naturally occurring sand (found on the beach) or could we use hydrophobic sand (Commercially sold as Magic Sand)?

No, avoid using sand that looks unnatural like it has been altered. We can not guarantee how the judges will view that. There are lots of natural sand types that can be used. The sand should not have any special properties like being hydrophobic.