backport.

src/main/java/com/gildedgames/the_aether/AetherConfig.java

@@ -33,6 +33,8 @@ public class AetherConfig {
 
 	private static boolean aether_start;
 
+	private static boolean disable_eternal_day;
+
 	public static void init(File location) {
 		File newFile = new File(location + "/aether" + "/AetherI.cfg");
 
@@ -79,6 +81,8 @@ public class AetherConfig {
 
 		repeat_sun_spirit_dialog = config.get("Misc", "If disabed, the Sun Spirit's dialog will only show once per world.", true).getBoolean(true);
 
+		disable_eternal_day = config.get("Misc", "Disables eternal day making time cycle in the Aether without having to kill the Sun Spirit. This is mainly intended for use in modpacks.", false).getBoolean(false);
+
 		config.save();
 	}
 
@@ -168,4 +172,9 @@ public class AetherConfig {
 	{
 		return aether_start;
 	}
+
+	public static boolean eternalDayDisabled()
+	{
+		return disable_eternal_day;
+	}
 }

src/main/java/com/gildedgames/the_aether/entities/bosses/sun_spirit/EntitySunSpirit.java

@@ -207,6 +207,8 @@ public class EntitySunSpirit extends EntityFlying implements IMob, IAetherBoss {
 
                 dungeonTarget.triggerAchievement(AchievementsAether.defeat_gold);
 
+                if (!AetherConfig.eternalDayDisabled())
+                {
                     if (!this.worldObj.isRemote)
                     {
                         if (!AetherData.getInstance(this.worldObj).isEternalDay())
@@ -214,6 +216,7 @@ public class EntitySunSpirit extends EntityFlying implements IMob, IAetherBoss {
                             AetherData.getInstance(this.worldObj).setEternalDay(true);
                         }
                     }
+                }
 
                 this.setDoor(Blocks.air);
                 this.unlockTreasure();

src/main/java/com/gildedgames/the_aether/world/AetherWorldProvider.java

@@ -34,6 +34,8 @@ public class AetherWorldProvider extends WorldProvider {
 
 	@Override
 	public float calculateCelestialAngle(long worldTime, float partialTicks)
+	{
+		if (!AetherConfig.eternalDayDisabled())
 		{
 			if (!this.worldObj.isRemote)
 			{
@@ -66,8 +68,9 @@ public class AetherWorldProvider extends WorldProvider {
 					data.setAetherTime(6000);
 				}
 			}
+		}
 
-		int i = (int)(this.aetherTime % 24000L);
+		int i = (int)(AetherConfig.eternalDayDisabled() ? worldTime : this.aetherTime % 24000L);
 
 		float f = ((float)i + partialTicks) / 24000.0F - 0.25F;