A DCC task is an operation that runs on a DCC Worker.  Examples of these include OCRing a specified group of documents, or searching a specified folder for documents to be OCRed.  Some tasks create child tasks, increasing the total number of tasks in the job.  As such, it is typical for the total number of tasks to increase while a job is running.  The DCC Scheduler breaks down jobs into different numbers of tasks based on characteristics of the specific documents being OCRed (number of pages, image sizes, etc).

The differences in the runtime may be due to the parameters used when scheduling the job, and the actual documents in the batch.  For example, when the "skip pages with text" option is enabled, the runtime will be proportional to the number of documents that don't have text.