WiFi access points reboot every day at the same time

I have four WiFi access points connected to a POE switch. They work fine, except that every day at exactly 9pm all four antennas reboot, causing the WiFi to go down for about a minute. Can anyone think of any reason why this would happen?! Here is a 1-minute video showing what happens: https://youtu.be/vxmjun6NU-g