Use this script to trim all selected layers with the duration you specified, you can also specify the gab you want between the layers ( in frames ).

Film Burn is an Animation Preset that automatically creates the overexposed "roll-out" effect, where the tail (and the head if you want) of a clip flickers into overexposure. By Stu Maschwitz

This script will allow you to select one or more layers and create a solid, choose the color and place it directly below the footage layer and it will trim the in and out points of the new solid to match the footage duration.