camediatiming

What's the effect of setting timeOffset when animating?

The CAMediaTiming Protocol defines a timeOffset property. Now, they say it's a time offset. It sounds straightforward, but howefer, when I set it to 15.0 for example, the animation still imediately starts. The timeOffset doesn't seem to have any effect. Maybe someone can point that out a little bit? ...

How to specify an beginTime for an animation by using CFTimeInterval?

For my understanding, beginTime can be used to say "hey, start at exactly 12:00 'o clock". But how would I tell this with an CFTimeInterval type? I thought that this one is nothing more than a kind of "float" value to specify seconds. Or what else would be then the difference to the timeOffset property that is specified in CAMediaTiming...