So if you're targeting say 60, then you need to replace about 30% of your water or 5700 gal. With a 27' round it looks like you need to lower your water level about 16" if you do it all in one go. If you do it in multiple stages you'd have to replace more water in total.
Pumping to waste is fast but if you don't have a main drain or can't shut off the skimmer then you won't get all that far. You could siphon with garden hose all you want, it's just going to be a little slower; I suppose you could do several in parallel.
Where is all this water going? Some jursidictions require that draining a pool has to go into the sewer, not on the ground or street (storm drain).
--paulr