Depends on the size of the pump However an average sise pump takes about 5 hours on an ave pool
If it is a vinyl liner pool you have to use a submersible pump. You can get a small one for right at $100.
You can hire a pump from your local hire shop or purchase a submersible one
USE A SUBMERSIBLE PUMP.
Throw a submersible pump in it and drain it to wherever you think is appropriate. These pumps are available from tool hire places at quite a reasonable rental.
You could use your pool pump. or get a submersible pump. it is also not difficult to siphon an above ground pool with a pool vacuum hose. all you need is somewhere to run the water to.
By opening the drain valve SLOWLY as not to cause a dangerous vortexI have worked on over 60,000 pools and have seen a drain valve once. The pool was built in the 30's on the coast and they used to pump sea water into it once a week and drain it to the ocean. I have drained pools by siphoning but you need enough grade to do this or a hillside behind the pool with a long enough hose to prevent soil erosion. You're better off renting a submersible pump.
The Northern Industrial Submersible Pump has the best reviews and ratings. It is 1326 GPH, 1/8 HP, 1in by their specs.
I just replaced mine it cost $350 when I was done.
Throw a submersible pump into the pool put the hose from it into a suitable drain and start her up. Take care that you don't have too much ground water as this could build up under an empty pool and lift it out of the ground and that would wreck it. even concrete pools.
There are several places to purchase a submersible water pump. Sears is a national retailer that sells the submersible water pump. There are also places online to purchase a submersible water pump such as Amazon, Water Pumps Direct, or Way Fair.
To compute the power of a submersible pump, you need the pressure and the pump power.
You can buy a timed switch mounted on the submersible pump. If you want to buy a submersible pump, you can choose VIDO's submersible pump, VIDO's submersible pump is of high quality and is the choice of most people.