For this I can only advise you to use a router with integration in HASS, it will be much more reactive than using nmap_tracker.
I bought a Xiaomi Router Mini for 24,67€ and wrote the integration for hass.
Using the router as a device tracker, the action are executed (in my case a light goes on) in about 1-5 seconds upon connection to the wifi.
And in addition it’s really a good router 
(only use this model if your internet speed is under 100Mbit/s, the wan port is limited to 100Mbit/s).