I noticed that hAP ac² reboots significantly longer after update than CCR1009 or RB2011. Is it because of 16mb flash thing?
+1 here!
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… 
i guess
maybe the cause of it’s wireless module
boot of old rb411 with @300Mhz is more faster
One thing I like about routerboards is the fast boot-up - my rb750gr3 takes exactly 30 seconds to log into winbox from power up.
I was thinking about picking up a hap ac2 and this is obviously not a deal breaker, but It would be nice if someone from mikrotik could chime in as to why this is the case?
Just curious what is the boot-up time now. Will a Hex S be faster than ac2? I need a solution for fast restoration after full power loss.