Custom Variable

I am simulating a scenario where a car goes over a speed braker at high speed and I want to measure the time and height it flew off from the ground. Can I setup a custom variable to measure this or is there already variables available to make use of?

You can use the minimaneuver commands to define new UAQs(variables) based on calculation from existing UAQs.
Predefined UAQs are listed on the Reference Manual(Chapter 24 ~ 26, depending on CarMaker version), and you will be able to find example usage of minimaneuvers relevant to your case on the document ProductExamples->BasicFunctions->RTExpressions.