Overriding the config_update_install_time is not currently possible as the feature is designed to prevent updates occurring during unscheduled times.
If you need to force an update to a device with the config_update_install_time config set out of band, wiping the Project Configuration is your only option. Doing this will remove the config_update_install_time config from the device, and then you can deploy an update immediately to update your device.