I do believe I've found out how to get a true delta time, and it doesn't even require an update.
First number number is dt
Second is FPS generated from it
Third is the internal fps expression.
Click to add another circle.
EDIT: Would everyone be willing to test these in your browser?
"Get Time" Delta
"Get Milliseconds" Delta
I can't offer the .capx for the second one. I had to monkey rig construct to make it.