I do not know how long they last but have never felt the need to replace one.
I do clean them ever so often, when they look a bit dirty.
It really depends on how one treats them.
When you pull them off the clean rubbers don't lay them somewhere in a dirty place but keep them clean, the two surfaces that touched the rubbers facing one another.
Do not offer them back up to the rubbers before you cleaned the rubbers after the session. If you can't wash the rubbers straight after the session , take the blade home, wash the rubbers and only then offer the sheets back on to the rubbers. Make sure the rubbers are dry and gently press all the air bubbles out.
This system works for me and applies to the protective films that are not sticky themselves.