Question: Trigger that controls timeline speed

Hello Everyone.

First, I'd like to say I enjoy reading your great tips in here, it helps a lot.

I have a question:

Is there a way to control the playback speed of the timeline in storyline 2 with a trigger?

Let's say I have  '+' and '- ' buttons and I want that clicking  '+' will make the animation faster, and '-' will slow it down, but it should be in loop.

Thank you very much.

Neta