You can do Triglav Panorama Hut to Hut Hike off-season as the Blejska and Uskovnica huts operate throughout the year. The best time to do this hike is in April or October when the other mountain chalets are closed, and the hiking conditions in the Julian Alps are still good.
If you are an experienced hiker and physically fit, you could also do this hike in winter, but the snow conditions would have to be stable, you would need additional equipment, and be prepared for the trek to be more demanding.