ME.
I had a rush hour test, 2 weeks before Christmas, and in the middle of a big town - think similar to Wolverhampton, Stoke-on-Trent, Coventry size, full of traffic controlled traffic islands, traffic lights, (and a different one for each lane,) and carriageways changing from one car to 2 cars wide, and then back to one.
It also had a one way system, And it was on roads that were a mixture of icy, and gritted, and slushy. It had put down 3-4" of snow the night before, and 10 minutes into my driving test, a fog began to form!
No problems at all! I had more time to think, and was able to relax a bit more, because everything was so slow moving. Massive advantage for me. 
Good luck to your son @1805 