If I understood it right:
deltaTime() is the amount of time between a frame.
1/deltaTime() gives you the frame rate.
Its mentioned in the example here https://fuzearena.com/help/view/lerp
Also, I think there is an update needed for the example:
I was starring at the line:

t += deltaTime() // duration

...until I had the idea, that it maybe would make more sense like this:

t += deltaTime() * 1 / duration

Not tested, but this should make the lerp-ing last for 5 secs, if the duration is set to 5.