Polar aerodrome fixes / Objective timer multiplier for difficulty

core/src/mindustry/game/Rules.java

@@ -101,6 +101,8 @@ public class Rules{
     public float buildSpeedMultiplier = 1f;
     /** Multiplier for percentage of materials refunded when deconstructing. */
     public float deconstructRefundMultiplier = 0.5f;
+    /** Multiplier for time in timer objectives. */
+    public float objectiveTimerMultiplier = 1f;
     /** No-build zone around enemy core radius. */
     public float enemyCoreBuildRadius = 400f;
     /** If true, no-build zones are calculated based on the closest core. */