From 6:00am to 12:00pm it is low tide, from 12:00pm to 6:00 pm it is high tide, from 6:00pm to 12:00am it is low tide, and from 12:00am to 6:00am it is high tide again. You get Snorunt in an ice room at low tide. You can also make Shell Bells using the ingredients you find at low and high tide.
Shoal Shell - High Tide
Shoal Salt - Low Tide
Get four of each, give them to the guy near the entrance and BAM! You have a Shell Bell!