I enjoyed Zion more than Bryce, but they have had to with the temperatures. When you visit Bryce, you are down in the canyons, and the temperatures are higher. At Zion, you are up in the pines atop the mesas, and it is cooler.
At this time of year, go prepared for any sort of temperature, it can be 100, or it can be snowing (rare, but it does happen). Generally, it will be cool in the morning, and warm up quickly. Keep in mind the altitude if you are from sea level, and watch your water intake. It is the high desert.