Does anyone know how long the garage will need my car for the first service at 10000 miles,?

Usually an hour.  But then the free wash and vacuum is much of that time.    The thing is is if it is getting taken to the workshop as soon as you hand the keys in and then go out with the service receptionist and check your car including wheels are damage free.  

mmm i never had a free wash and vacuum at dealer maintenance And usually is a morning drop appointment and an afternoon pickup.

You are best asking the garage its booked in at. 

In theory an hour or so but all manor of delays could happen that pushes your ramp slot back, especially if you aren't first job of the day. This is why they often won't commit to a time slot and say they will call when it is ready.
You also need to factor in any of the 'free' wash/valet & health check services that they may be offering.
 

 

 

They’ll ask you to drop the car off first thing. And leave it with them all day.

 

For some reason they find it difficult to schedule accurately in a way that would help all the customers.

 

Its a real PITA.