Can I set duration of multiple After Effects (freezed frame) layers to a fixes value (e.g. 4 seconds each) at once?
Select all of the layers. Move the time cursor to where you want the layers duration to end. Press alt + ]. This will extend your layer to that position (if it is able to be extended).
Pressing alt + [ would adjust the in point
Pressing Press [ or ] on their own would move the in or out point of the layer to your current time position.