I used to change every two days and that was fine, now change every three days, but do find, like a few others, that start to get erratic readings sometimes, so might go back to changing every two days.
I can only use metal ones & have to change every 2 days. If I leave it an extra 6-8 hours, I end up with sores where the needle was.
The plastic ones made me sore within hours of inserting, which is why I have metal only. Have been on a Medtronic pump now for 5 years.