Contact lenses: if I wear them for too long will they damage my eyes?

Yes. Yes overuse can lead to contact lens overwear (irritation, redness, etc), as well as increased risk for corneal infections (which can permanently cause vision loss), decreased oxygenation (corneal pannus), and the lenses can tear after used beyond what they are supposed to be used.
Yes. Yes if worn too long for whatever your eyes can tolerate, it can cause corneal edema, dryness, inflammations, and/or infections.