I can confirm this for my Elite ESL-2 system with the ESL 2 APP Kit module. Reaction seems instant as soon as the led on the sensor goes on the HA App on iPhone shows the detection
@Wibble
If you get an ESL-2 board then you need the ESL-2 APP POD instead of the IP Module.
Quote from AAP
Sweet, so for that one you would need to use the ESL-2 APP POD if you have an ESL-2 or the older IP-MODULE which was used on the old panels.
Make sure you don’t get your hands on the IoT-MODULE or ESL-2 IOT which is our new phone app module, the firmware will not work on these.
Not sure if a loom cable is required for the ESL-2 board my installer only had the DLINK cable which I borrowed to install the mentioned firmware.