The biggest rule to remember when you’re running late for an audition is do not call the casting director!
I know, it’s tough. You could already be stressed to the gills when you’re suddenly stuck behind an accident, your kid just threw up, or you can’t find parking. You’ve worked hard, you had to borrow an outfit, and you’re balancing between that level of “I know it” and “I know it so much it’s lost all meaning”.
And then: wha-bam!
Logically, it would make sense to call the place you’re going to when you’re running behind. But casting houses are busy. They’re dealing with directors, submissions, agents, prepping jobs, running sessions, problem solving issues, etc.
Call your agent. That’s what they’re there for. If you’re going in for a commercial, there may be wiggle room depending on how long the session for your category is running. If it’s TV or film, you may be SOL; they don’t run on the same time frames. If that happens, see if they’ll accept a self tape. If not, allow yourself all the feels, whatever they may be, and know there’s another one coming down the road.