yet another attempt at mines

src/engine/workthreads/MineThread.java

@@ -116,7 +116,7 @@ public class MineThread  implements Runnable {
 
             //check if this mine needs to open
             LocalDateTime openTime = LocalDateTime.now().withHour(mine.liveHour).withMinute(mine.liveMinute).withSecond(0).withNano(0);
-            if(currentTime.isAfter(openTime) && !mine.wasOpened){
+            if(currentTime.isAfter(openTime) && currentTime.isBefore(openTime.plusMinutes(30)) && !mine.wasOpened){
                 mineWindowOpen(mine); //hour and minute match, time to open the window
                 ChatManager.chatSystemChannel(mine.getParentZone().getName() + " " +  mine.getMineType() + "MINE is now vulnerable to attack!");
                 continue;