Event is a container for a clip. You can trim it, split etc, but the original media remains untouched. You just change in/out points. In your case, right click the event and choose Create Subclip. This will create virtual 10-second clip.
Vegasaur can also do it. Though it doesn’t contain a dedicated “Photo Montage” tool (at least for now), its Pan/Crop Assistant and Quick Properties can perform this type of work with ease.