I am creating a shader in Reality Kit Pro that sets a material's opacity
based on the texture coordinate y-value and how much time has elapsed
since TimeStart. The Time node below is the current ``animation time:''
In my Swift code I want to set the TimeStart parameter to initiate the animation.
The problem is I do not know "what time it is" according to the Time node.
For example, if I want to start my animation in 3 seconds from the current time what
value of the TimeStart parameter should I use?