Dragon Hourglass

Structure
It is a gigantic hourglass, approximately 7 meters tall, with red sand enshrined. It is decorated and gives off an indescribably divine aura. One exists in each country where the calamity will strike.

Purpose
It indicates the when the next Calamity Wave will strike/arrive and it also transports the four heroes (bow, spear, sword and shield hero) and their respective party's to the region that the Calamity has struck. Not much else is known other than what was mentioned in the series.

When the final grains of sand from the hourglass drips down, the Calamity Wave begins. As stated earlier the four heroes and their respective party's are transported to a particular hourglass that is in range with the Calamity Wave. The first few Waves only depict the calamity's event in Melromarc, whereas the calamity strikes in multiple regions all at once; it is unknown who exactly took care of each region that the hero's did not defend, nor if the Heroes actions stopped the waves in other regions.

The hourglass is needed to perform a class-up. Almost all regions, whether it be human inhabited, Demi-human ruled, or a completely uninhabited region, all have this similar Dragon Engraved Hourglasses that can perform the same function. Mostly they reside within that country's capital or a capital itself is built around where the Hourglass resides. That country's government alone decides who will get to class up; not simply anyone is permitted to do so. By using special items, one can modify the class advancement procedure like Fitoria's gift of Ahoge to Filo which doubled all the statuses of Naofumi's party, which was quiet rare.

The dragon hourglass can also reset the levels of an individual back to Level 1. It is mostly used on criminals.

But the heroes must sync with said hourglass before they and their associates can be summoned to that country's wave. When registered, the heroes get the display of the time of the calamity. But it doesn't predict the region(s) where the calamity is going to for sure hit.

By the end of the series all of the Red Dragon hour Glass stopped instantly, indicating the heroes victory over the wave. It was then expected to be just only be used for class up.

Regions
One is shown inside Melromarc's Castle Town's town plaza in the middle of the church.

Another was also shown to be in the underwater submerged temple of Cal Mira Archipelago.

It was also shown to be in the hidden country protected by Fitoria; Fitoria also mentions that there are numerous hour glass across the world and that she manages the region where there is no human settlement.

Chronology
Naofumi wasn't aware of how the system works at first. He was told about the Dragon Hourglass in Melromarc's church and went there. He got himself unknowingly registered to the Melromarc Hour glass, when he actually meant to check for the time of the next wave. Naofumi was under the impression that he will be teleported to the region that the wave occurs. But that wasn't the case, as Melromarc's hourglass merely transports heroes to the wave affected region within its jurisdiction. The heroes must register to the hour glass of that particular country to fight the waves. When he was framed for kidnapping Princess Melty, he was worried that even if he ran to another country, he might be teleported back to Melromarc during the time of the next wave and might be arrested, not knowing that he could have easily unregistered by registering in other country's hour glass.

Trivia

 * Their origin was a mystery as all the records of it were destroyed or forgotten in course of time.