Geoff Keighly recently tweeted about the length of Nintendo's press conference, which will be held just a few hours before Sony takes the stage at E3. It is expected that Nintendo will reveal their much anticipated 3Ds handheld , amongst other things.
"Just got my Nintendo E3 invite. Looks like they are doing a 2 hour briefing from 9-11 AM. Guess this is why Sony now starts at noon."