it is done

core/src/mindustry/entities/traits/TimeTrait.java

@@ -0,0 +1,23 @@
+package mindustry.entities.traits;
+
+import arc.math.Mathf;
+import arc.util.Time;
+
+public interface TimeTrait extends ScaleTrait, Entity{
+
+    float lifetime();
+
+    void time(float time);
+
+    float time();
+
+    default void updateTime(){
+        time(Mathf.clamp(time() + Time.delta(), 0, lifetime()));
+
+        if(time() >= lifetime()){
+            remove();
+        }
+    }
+
+    //fin() is not implemented due to compiler issues with iOS/RoboVM
+}