Why is deltaTime different in BP and C++?

My point is that Sleep(1000) causes the game to run at ~1 fps

In C++ tick this is clamped to 1/2.5 sec

In BluePrint this is clamped to 1/8 sec

So my question is why they are clamped differently?

Are these clamps arbitrary?

Or are they documented somewhere?

Should C++ code substep up to when fps drops down to 2.5 fps
While BP should only substep up to when fps drops down to 8 fps

Is it documented somewhere what actually happens if the fps drops?

Dragging & moving the window with the mouse causes a temporary freeze in most programs and I don’t want this to potentially cause things to go out of sync!

I want to know the best way to deal with this!