The sands of time is another way of referring to time. It is more poetic and is often used when talking about how time passes.
"I am always ready to score the winning goal," said the footballer, dismissing those who said the sands of time are running out on his long career.
Plan for your retirement. The sands of time catch up with everyone.
To draw a line in the sand means to create an imaginary boundary or 'line' that cannot be crossed without causing problems.
Mary drew a line in the sand. If her son didn't do his homework on Monday, he would have to stay at home for a month.
Much of Namibia is covered in desert. The country also has grasslands and a Central Plateau which is quite dry, large areas of which are used for livestock farming.