As a DJ, I use the M44-7 cartridge and I was just wondering how often the stylus should be replaced. I do a lot of scratching and spin LPs an average of 2 hours per day.
For home use, a stylus wears out in 600 to 800 hours. For DJ use, they can wear out quicker, say in 300 to 600 hours. At 2 hours per day, 300 hours is five months. So in your case, we suggest replacing the stylus every six months.
But do it sooner if you start to hear poor audio. Perhaps keep one new stylus as your test standard and compare the sound of a "worn" stylus to the new test stylus.
The PDF attachments below contains photos of styli with different stages of wear.