Funny you mention this because since couple of weeks I have exactly same impression on hap ac2!
And each time you reboot, you think something is wrong and device is hanging!
I just right now timed from pressing reboot to Wifi visible: 1Minute 48 seconds, hap ac2 with 6.43.7 (no additional boot delay, no additional SW package etc.)
That is a lot compared to other models!!!
I have also the impression it was faster in previous SW versions but never measured it really before today
I have link monitoring scripts on all MikroTiks that beep using beeper (if present) when any neighbour is down. When I update ROS I reboot all router at once to minimize downtime. And always all other routers keep beeping for few seconds after reboot because they're all waiting for hAP ac2 that always takes its time and doesn't see any reason to hurry up...