Busy, but you will be crawling along and have a reasonable amount of thinking time. Roundabouts/junctions can be annoying tho! Guess in London it will be busy anyway.
I did mine at 8.10, and it lasted for a good 50 minutes. Guess he just had a preplanned route that he was sticking to it as long as it took.
My first (failed) test was also at that time and it was much shorter but maybe she cut it short as I made my serious error near the start!
I've been told you can go forward twice on reverse round the corner to straighten up. Either way keep an eye so you don't go out over the other lane. On most medium angle ones 1 full turn should do you. I always used that as the guideline and adjusted it as I went along (SLOW, REMEMBER OBSERVATIONS).
Think of the really sharp ones like bay parks ie pretty much full lock.
The more practice the better. Midway through a manoeuvre I found it can be tempting to over adjust and confuse yourself with how many turns the wheel has done. As you practise you learn to recognise the stages.
If you drive well normally just relax and go with the flow
Good luck!!