-do you mean boot time for core/hybrid ? ...if so you're sort of missing the point, ie LMCE is a HUGE piece of software which is designed to be on 24/7 and control the whole home ,it's not solely a media centre (even if as I suspect , a lot of us use it that way) ..So actual boot time is irrelevant ' )
If you mean start up time of a media director, I think that's largely down to limitations of PXE /hardware/AND , once more , the size (and capability) of the system......so it's a little like asking the 0-60
mph time of a mobile crane !
Having said that I believe there have been discussions about MD start up times/resuming from standby etc,
as there is a (valid ?) train of thought that an MD "should" behave like an appliance, and start in as short a time as possible..-personally ,I believe that although that's desirable,it's not all that important,as it gives me time for a bathroom visit before i get into bed !!