I think 5 seconds is more than enough (and I mean from bootloader to the starting of init). I think the “norm” might be around three seconds (again, from pressing enter on your bootloader to getting your init’s welcome message—e.g., “INIT: version 2.86 booting”). You can shave as much off as possible by compiling most things (even most things “necessary” for your computer) as modules. The only things you really shouldn’t compile as modules are your filesystem driver, the driver for however your block device is interfaced to the hardware (e.g., ide/sata), and of course the driver for ttyUSB.

Once you get to init, you may begin printing custom text to your device (implementing this by patching your init or creating your own pre-init). The majority of “boot time” is actually time spent after init has loaded, so you won’t lose much.

Thanks osor, now that sounds like it should do exactly what I need, and more easily than the method in the book.

The LCD allows you to make a "power on" screen. Something that is displayed as soon as the LCD receives power, and it remains there until you clear or write other information to the LCD. So from the time the power button is pressed to the time the system gets to init and starts writing out to the LCD I could make it say something like "Booting Asterisk Server."

I'll start reading up on init and see where that gets me. Thanks for all the help and ideas everyone!