The boot time is dependent on a bunch of stuff that is application/RTOS specific but you should be able to measure that for your own application by toggling a GPIO pin in your first task.
Other timing information WRT the RTOS is at:
C:\Freescale\Freescale MQX 3.8\mqx\examples\benchmrk\timing\results\iar\twrk60n512\twrk60n512_intflash_release.html
An old diagram of the boot process is:

Regards,
David