Need to schedule a job much like cron

It's pretty simple create a custom schedule job. The below link will be helpful and also refer the customizer guide, it is very well explained there too.

Creating custom scheduled jobs

You can create your own Scheduling queue which can appear in Queue Management. Below is the example to create scheduling queue.

public static void processPublishingQueueEntry(WTObject wtobj, String objno, String objrev, WTObject wtobj2, String objno2, String objrev2) {

  SessionContext prev = SessionContext.newContext();

  try {

  SessionHelper.manager.setAdministrator();

  ReferenceFactory referencefactory = new ReferenceFactory();

  String sobj = referencefactory.getReferenceString(wtobj);

  String sobj2 = referencefactory.getReferenceString(wtobj2);

  QuerySpec spec = new QuerySpec(wt.queue.ScheduleQueue.class);

  spec.appendWhere(new SearchCondition(wt.queue.ScheduleQueue.class, "name", SearchCondition.EQUAL, "yourqueuename"));

  QueryResult result = PersistenceHelper.manager.find(spec);

  ScheduleQueue queue;

  if (result == null || result.size() < 1) {

  //Create the Queue.

  logger.debug("Creating a New Queue, as its not present.");

  queue = QueueHelper.manager.createScheduleQueue("yourqueuename");

  } else {

  logger.debug("Using the existing queue.");

  queue = (ScheduleQueue) result.nextElement();

  }

  WTUser adminUser = (WTUser) wt.session.SessionHelper.manager.getPrincipal();

  Class[] argTypes = {String.class, String.class, String.class, String.class, String.class, String.class};

  Object[] argValues = {sobj, objno, objrev, sobj2, objno2, objrev2};

  Timestamp timestamp = new Timestamp(System.currentTimeMillis() + 5000L);

  queue.addEntry(adminUser, "createViewable", "com.xxxx.services.xxxxService", argTypes, argValues, timestamp);

  } catch (Exception e) {

  e.printStackTrace();

  } finally {

  SessionContext.setContext(prev);

  }

    }

Hope this will help in creating job with in Windchill