I have added a personal message to the startup screen showing my name & phone number if found. The problem is that the screen remains too dark to read the message until the device has fully booted when the message is visible for a fraction of a second.

Is there a hack to make the startup screen illuminate whilst the device is booting?

Did you try to extent the time (Set the display number to the minimum number of seconds your message is displayed)

<!-- Edit this file to display a message while your unit is powering on -->
<!-- Allow one full power cycle after editing for your message to be updated -->

<!-- Set the display number to the minimum number of seconds your message is displayed -->
<display = 0>

<!-- Type your message on the next line -->