FYI, the timers in stores may be compatible with HomeKit once Orbit releases the firmware update. I noticed that the packaging on shelves hasn’t been updated with the new timer image and still only show the A,B,C program button, but if you open the package it will likely be the newer timer with the A,B,C,D program button. I checked my local Home Depot and Lowe’s and they were both stocked with the new timer.
My guess is that Orbit is waiting for the timers to be HomeKit compatible out-of-the-box before updating the packaging with the “Works with Apple HomeKit” badge. Now we just wait patiently for the firmware update.