Thabks for the link ! Got the code accessible for this kiosk picture frame by any chance ?
Reading the first article it seems like OP could benefit from using start_cd.elf (3rd stage bootloader, but with the graphic subsystem removed), they report a 0.5s improvement in loading time
- https://www.furkantokac.com/rpi3-fast-boot-less-than-2-secon...
- http://himeshp.blogspot.com/2018/08/fast-boot-with-raspberry...
I used these two to make a digital photo frame with a Pi that boots very quickly to a browser in kiosk mode. If you have very minimal requirements, you can get some very impressive boot times.