Whisk together orange juice and zest, garlic, thyme, mustard, 1 teaspoon salt, and 1/2 teaspoon pepper in a large bowl. Whisking constantly, pour in oil in a slow, steady stream; whisk until emulsified. Add pork; toss to coat. Cover bowl with plastic wrap, and let pork marinate 20 minutes at room temperature
Heat a grill or grill pan until medium-hot. Thread 5 or 6 cubes of pork onto each of 4 skewers; season with salt and pepper. Discard marinade. Grill pork, turning occasionally, until cooked through and slightly charred, about 12 minutes. Garnish with thyme sprigs, and serve with orange wedges.