Check out this document. It goes through some basic boot time quantification on the LH7A404-11, which is going to be very comparable to the LH7A400-10.
http://www.logicpd.com/downloads/682/1003251_Rev_A.pdf
120 Seconds seems very suspicious. Are you sure you have not created any custom code with incorrect use of 'wait' functions? Also, are you sure you have used the most up to date drivers that we have released? I would suggest comparing the drivers you are using currently with what is on our download site now.
The best practice to figure out an issue like this is to start with a very basic image. No custom apps or drivers, just a simple image with the drivers you need. Find if this boots ok and then begin adding your custom stuff and also more components from Platform Builder.