By setting durations on your Pages, you can let Spark do the work, as overlays will automatically animate out once the timer on an overlay has expired.
If Looping is turned on for the layer, the overlays with timers will go on/off back-to-back of one another.
1 - Edit the overlay to set a timer
Make sure you're in Edit Mode and click on an overlay you want to set a timer for to open it's Overlay Editor.
2 - Type an integer into the Duration field
At the bottom of the Overlay Editor window, you'll see a Duration field, measured in seconds. Type in how many seconds you want the overlay to stay on-stream for. This should be an integer, so positive, whole numbers please!
3 - Click the Save
Hit the "Save" button in the bottom right
4 - Play the overlay
Play the overlay and watch how it automatically animates off after the timer meter has expired.
You'll see that the overlay you just edited now has a small grey progress bar at the bottom of it. That's your indication that this overlay has been assigned a Duration. When you're back in On-Air Mode and take that overlay to air, that progress bar will fill up. Once its completely full, the Duration has expired and the overlay will automatically animate off. If Looping is turned on, it will automatically play the next overlay on that layer that has a duration.