My one attempt to treat at night was a stinging disaster. First, it was a hot day and still hot in the evening. I had used a bee escape to get as many bees as possible from the supers into the main brood box. They were crowded and hot, so: Second, there were many, many bees bearding the hive, so I couldn't get them all anyway. And then Third, my battery was low on juice, so I had to repeat the process. The bees were not happy, and let me know about it as I put the supers back on.
I've decided to wait for cooler weather, and to do my treating during the day when I can see what I'm doing.