I'm using monthly disposable soft lenses. My ophthalmologist recommends replacing them every month. But I've regularly used one pair for 4 months, sometimes even 6 months. I've been doing this for last 14 years now. I don't wear them constantly- I use them for about 10 to 12 hours a day, 6 days a week, and rub+rinse+soak them in opti-free every night.
My ophthalmologist doesn't know I'm doing this. I go for routine checkups once every year, and he's never found a problem with my eyes.
Realistically, is it that important to replace contact lenses on a routine planned schedule? If I've not had a problem in 14 years, it doesn't seem like I'm significantly increasing the risk of eye diseases by not following the replacement schedule. Perhaps I will get an infection some time in the future, but then every contact lens user will probably get one infection after 14+ years using them.
Read more: How bad is it to extend disposable contact lens life?