@4DEE One shot bursts are definitely spawn behaviors we are looking at adding in the future. Are there any other spawn behaviors you would like to see?
The delay on the periodic burst mode happens before the first spawn, so that is why you didn’t see any particles spawn. We should make that more clear. 
For right now though, you can use capacity, high spawn rates and timers to make your own one shot.
In the attached images I expose the spawn rate and control it in the visual scripting graph. I use the capacity in the VFX Graph as the size of my one shot burst. When I tap the screen I set the spawn rate to a value much higher than my capacity. After 0.5 second I set the spawn rate back down to 0.
