I've just got back from the 'Ring yesterday, driving there in a day is do-able, best to drive there one day 'ring the next and then drive back the following day - but I know that next time. There is also some lovely countryside to see in the Nurburg area.
I drove the Ring, then left at 3pm to make the 8pm Calais-Dover ferry(France is one hour in front of the UK), was a bit late for that one but they give you a two hour window each side of your booking time so it's not crucial you are on time. 90 minutes on the ferry then the trip home, I was in bed by midnight our time.
The cost of lap tickets at the 'ring are 64 Euros per 4 lap ticket. Ferry was £70 ish because of the early out/late back. It was about 300 miles from Calais to Nurburg and took about 5h:40m - so call it 6 hours.,