It really depends on the application.

With the similar/even weaker socs (imx6 etc..), in the automotive domain, we used to target sub 5 second latency.. we had to get rid of things like even init and directly start the application..

Eg: 1.5 seconds here: https://youtu.be/QbEYhQIjlQc

There's a popular slide deck[1] with common techniques for paring it back too.

[1] https://bootlin.com/doc/training/boot-time/boot-time-slides....