Request all active users in the last 3 minutes

src/main/java/de/thm/arsnova/services/StatisticsService.java

@@ -22,12 +22,14 @@ public class StatisticsService implements IStatisticsService {
 
 	@Override
 	public final Statistics getStatistics() {
+		long since = System.currentTimeMillis() - DURATION_IN_MILLIS;
+		
 		Statistics statistics = new Statistics();
 		statistics.setOpenSessions(databaseDao.countOpenSessions());
 		statistics.setClosedSessions(databaseDao.countClosedSessions());
 		statistics.setAnswers(databaseDao.countAnswers());
 		statistics.setQuestions(databaseDao.countQuestions());
-		statistics.setActiveUsers(databaseDao.countActiveUsers(DURATION_IN_MILLIS));
+		statistics.setActiveUsers(databaseDao.countActiveUsers(since));
 		return statistics;
 	}
 }