Im pretty sure on the default system image and setup of these machines – someone forgot to set the default boot drive. Every time you install the OS or image an OS on to the drive – you have to ‘Bless’ the main drive. If you don’t, this can cause slow boot ups, especially if you have other drives attached, since the boot loader must search the disks for valid boot disks before moving on.
Under System Preferences, select ‘Startup Disk’, then ‘Macintosh HD’ (or whatever your default boot volume is), and hit restart. Thats it!
This is a super easy fix, and easily cut my 1.5 minute boot time into about 25 seconds.