OMG! I didn't even think of this. Here's how I imaging it might go:

  [CAR] Sir, I need to visit the service center and will be gone for about 1.5 hours.  Is that OK?
  [ME] Will you be back before I need to go home?
  [CAR] According to the traffic patterns and the availability of the service tech's I'm 98% sure that I can return by 5:00PM.
  [ME] OK.  Have fun!
  [CAR] Thank you, sir.