I arrived too late for the 8:30am Shuttle to Echo Canyon trailhead, so decided to set off backwards. After securing a campground space for the night I set off from the visitor center at around 10:30 on the Rhyolite Canyon trail to Serah Deming Trail, and on to Heart of Rocks trail junction. I didn't see anyone else on the trail until approaching the Heart of Rocks Junction, but then met up with several couples and single hikers, all of whom had started on the morning's shuttle.
The weather was sunny with a slightly hazy blue sky, and the temperature was in the 50's. Very pleasant out of the wind and shadows, but a little cool otherwise. It was the perfect temperature while moving, but a little on the chilly side when stopped. Regardless, I lingered to take photos, and as I did so, all the others on Heart of Rocks passd me. I stepped off the trail in the sunny lee side of a rock to enjoy a quiet and peaceful lunch, then completed Heart of Rocks and continued on Sarah Deming out to Echo Canyon. Around 3pm the lengthening shadows and increasing altitude decreased the sun's warming benefit and it became increasingly uncomfortable to stop even for brief photo sessions, especially when my camera became cold enough to represent it's batteries as being empty, even after a new set was inserted. The uphill exertion kept me warm enough hiking though.
At Echo Canyon trailhead I got lucky on a ride back to the visitor center with some returning day trippers, but I would recommend that you have more firm plan for getting back to vehicle than I did, or arrive early enough for the 8:30am hiker shuttle to Echo and hike the easier (downhill) route back to the visitor center. Back at the car, I returned to Massai Point to await the sunset. It was extremely windy and cold up there, but I finally managed to secure the camera inside my wind shirt long enough to coax out a couple of final sunset shots from the 1/4 mile nature trail. After which, I called it a day and returned to my campsite, where the lower elevation and lack of wind made for a fairly pleasant evening of food chores.