Travelling to Qingdao to take delivery of a ship two of my daughters will accompany me as tourists

I am to travel to Qingdao to take delivery of a ship from Qingdao Beihai shipyard. I intend to take two of my daughters with me. After I take delivery of the ship (approximately 15 days after arriving in Qingdao), my daughters will return home by air and I will leave China on board the ship.
In this case, my daughters would require to obtain a Tourist visa. Please advise whether item-4. 'Confirmed return flight ticket and its photocopy' is necessary.
As the exact date of delivery of the ship is not yet fixed (due to delays caused by rain etc.), it is not possible to purchase tickets much in advance. Is this is a rigid requirement.
If the visa is applied and obtained, what is the validity (within how many days must the person travel?)