I think the default is set to 5 seconds but do a seach here and on the scripts forum and you'll find several threads decribing what your looking for. Should be a script on the vaast site that allows you to preset your pic and crossfade length. to however you wish.
Before you drag them to the timeline, go to Options -> Preferences, and choose the Editing tab. Set New Still Image length to how many seconds you want the images to be. For automatic crossfades, check the box marked Automatically overlap multiple, etc, and adjust the cut-to-overlap conversion option to set how much you want the images to overlap.
Click OK, then select all your images and drag them to the timeline.