How to change speed of game in real time using GUI Slider?

I am setting up a project where I need to test a few variables. I have lighting and gravity changing in real time using GUI sliders.

I want to know be able to change the overall speed of the game using a slider. Searching forums and google, i couldn’t come up with an answer.

Is this even possible? If so, how would I go about doing this?

Thanks

http://answers.unity3d.com/questions/278068/help-with-my-speeding-up-time-script.html

Googled ‘unity game speed’ and got that link, amongst others.