After 250hrs+ of use. There is also the new Tweel Turf exclusively for Deere mowers.
Just got some more info on them. There is an official warranty now that covers them for the life of the first tread or 5 years. Operating environment for warranty is -40* through 240* so I think most people will be okay. It doesn't cover damage obviously but does cover any sort of defect. They do also officially state the Tweel will operate fine with damaged spokes and that it should be at the operators discretion when to remove them from service (feeling unstable, poor performance, etc).