What is the wort made from? I've done a lot of fermenting over the years off all kinds of stuff, beer, wine, mead, shine. I'd think if anything the airstone would speed up fermentation substantially.
Primary fermentation usually only lasts about 3-5 days unless you ferment cold with a slowburner yeast like lager yeast. After that Co2 output drops significantly. Especially with simple sugars involved. More complex sugars can ferment longer, but heat and aeration is usually not good unless you want to ferment the sugars as fast as possible.