The Smooth Delta Time node returns the change of time between two frames, this frame we are on and the one before. This node also does another step and tries to account for lag or stutters, smoothly changing the amount of time to match that change.
At this current time, Resonite uses Unity, so this Unity Documentation about Smooth Delta Time may be relevant in helping understand what this does. And following that, this has an excellent explanation about Time Frame Management, which in general may help with working with this node in your content.
Uses
Using this node, you can make an accumulator or a timer using the frames here and storing them to a variable and adding them every frame.
Outputs
* (float)
The smoothed difference in time between this frame and the last frame.