Someone cant tell me which stage the bootchart end ?

I want to optimize the boot time for android10, so I using bootchart tools to build image below. But I don't know which stage end?
I search Internet someone said the bootchart just show the time after init process not include bootloader and kernel, and I don't know what stage it end.
And another question is where every using bootchart I get different time in bootchart ?

https://drive.google.com/file/d/1wkhMeR7KykAr-efPJuR-H45IKGL5dvLm/view?usp=sharing