Hi Lorraine,
Per Item means that each item will stay on-air for the duration of that item as controlled by the length of the scene director for the scene the item is built from.
Per Item (Fixed) means that each item will stay on-air for a fixed duration, ignoring the scene director length. All items will use the same fixed length.
Per Group controls how long it takes for all items in the group to cycle on. i.e. Each item will be onair for the group length divided by the number of items in the group.
To achieve what you are trying to do, I believe you should set the mode to "Per Item". Make sure the scene director in the scenes is at least as long as you want the items to be online for. You can do this by lengthening the animation controller on the scene director,or adding an event on the scene director to make it longer. If in your group you want the item to play for less time, you can click on the item in the group and go to the "Scene Control" tab and adjust the "Play Range" setting to choose how many frames you want to play. You'll see the duration column in the sequence change and display the new duration..
If you can't figure this out, let me know and I could make a quick demo video for you.
#XPression