Agree! The ability to select multiple items on the screen will save time in the designing/layouting process too!

Indeed. In fact as an example the developers of the Doodly interface should examining the Prezi interface. It would be great to select multiple items based on a selected area on the screen. Productivity would be much higher.

I support this and would add to it. Given I have selected a group using ctrl-click, when I manually enter a value for the delay or duration settings on any one of them, then the relevant setting on every grouped item is updated to the same value and... when I adjust a value for the delay or duration settings on any one of them, then the relevant setting on every grouped item is adjusted by the same amount and... when I drag and reposition any one of the grouped items in the layers panel then every grouped item is dragged and re-positioned to the new layer location, keeping their own relative layer position when they do so

As a note, you can right-click and select all. Then, go to the gear icon at the top to set the duration for all assets on the canvas.