Unlike Cisco 2960-X switches, 802.3az does not come enabled by default on Juniper EX3300 models. Use ether-options ieee-802-3az under the interface-range tree to enable this energy saving protocol.

interfaces {
    interface-range WIRED_PORTS {
        member-range ge-0/0/0 to ge-0/0/47;
        ether-options {
            ieee-802-3az-eee;
        }
    }
}

When committing this option, we noticed around 8 seconds of connectivity loss for 96 wired connected hosts. Be careful when enabling this in a production setting.