Is task completion status measured by number of hours spent on the task or by percentage which is inserted by the user/employee?

How often a user/employee is required to update task completion status? Is there any automated reminder that requests update for task status? What if the employee doesn't update or forget to update the task status? Will admin of Zoho project account be in the same situation like in real life when no one reports about the progress unless boss request the status report?

  

Is it possible to create a task where starting date is defined but ending date is left undefined, if I don't know about realistic amount of time required for certain tasks to complete?

When we define or enter starting and ending date of a task while creating one, 

- Are we setting general time framework for the task within that an employee must complete the task and during that the employee can do another jobs also if there is a time for him or if he can manage it or he want it?  

- Or are we setting a time limit only for this particular task during which the employee shouldn't do any other job if he/she has not yet completed the task? 

Could you show me some cases how to use zoho projects?