Many roguelike games have an incentive for the player to keep moving, to discourage super slow and cautious play, such as a limited supply of food or location-based hazards that need to be avoided by moving to the next area.
In Ragnarok, the hazard is... well... RAGNAROK! It's the end of the world as we know it, and you may feel fine, but you certainly won't if the evil gods have their way. The good gods are at a disadvantage since they lost all their toys. Time is ticking, go find some artifacts!
According to legend, Heimdall's horn Gjall signals the onset of the final battle Ragnarok. This is indeed true: using the horn yourself immediately advances the turn counter to 22,000. When you hand it to Heimdall on Bifrost, the turn count will advance to 23,000.
When the turn counter reaches 22,000, either because you used Gjall or time passing naturally, you will receive a popup narration as follows:
You hear a terrifying cry from Heimdall: "O great heroes of the world!" "I must have Gjall to rally the forces of good." "Time begins to grow short. The sea rages with the anger of Jormungand." "The earth quakes mightily. Loki seems ready to burst his bonds." "The moon and sun shall soon be swallowed by the mighty wolves Fenrir and Garm." "Surtr is honing his sword of destruction. The evil ones are gathering their forces." "To speed you in your quest, I will use my powers over nature." "The lesser creatures of the realm shall grow weary and despair." "They shall no longer wish to battle against your might."
When the turn counter reaches 25,000, a further popup narration appears:
You hear the crowing of the three cocks; the final battle is at hand. Odin projects hit astral image to you and booms mightily: "Many days will the gods battle fiercely with the forces of death." "Make haste to reach Asgard, but take care as well." "You are the only hope we have left." "Aid us and join the ranks of mortals who have been honored with greatness." "Fail and the universe shall perish." "First, take Gjall to Heimdall at Bifrost or we shall be overwhelmed." "We await you at Vigrid."
On some earlier versions of the game, the evil gods will automatically win at about turn 26,000, causing your game to end. On the latest version 2.5, this loss condition is no longer present, and you can wait as long as you like (tested through turn 40,000).
The battle begins as soon as you reach Vigrid, leaving you about 80 turns to deliver all remaining artifacts. Chug a few potions of speed and wear an amulet of quickening before venturing into Vigrid, because now every second counts! Also, the evil gods will instantly kill you if you step next to them. Don't do that. Locus mastery is useless here, so teleport at your own risk.
Items of note
The two cubes, blue and grey, can manipulate time in less drastic amounts. The blue cube randomly rewinds the turn counter by 1-100 turns; this effect happens roughly every 200 turns while it's in your main inventory. This is incredibly helpful! On average, the blue cube will extend your remaining turn count by about 25%. The grey cube, on the other hand, advances the turn counter by 1-500 turns when it fires; which is terrible. There is no reason to ever pick up the grey cube unless you plan to enchant it into the orange cube in order to reach the Wasteland.
Manipulating one's speed is also a way to buy additional time. This can be accomplished by using one or more of: an amulet of quickening, a potion of speed, or polymorphing oneself into a faster creature (such as a swordsman).