Set InitialSpawnDelay to 0

and set the value to 1500 in the default mods.

OpenRA.Mods.Common/Traits/World/CrateSpawner.cs

@@ -29,7 +29,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly int SpawnInterval = 180 * 25;
 
 		[Desc("Delay (in ticks) before the first crate spawns.")]
-		public readonly int InitialSpawnDelay = 300 * 25;
+		public readonly int InitialSpawnDelay = 0;
 
 		[Desc("Which terrain types can we drop on?")]
 		public readonly HashSet<string> ValidGround = new HashSet<string> { "Clear", "Rough", "Road", "Ore", "Beach" };