This is a good ploy for enduring long waits. I went to Dulwich for my blood test, took my ticket, and I had about 20 people in front of me. I calculated how long each person took and realised I had around 30 minutes, so I went off and had a delicious coffee at one of the many coffee houses in ED, came back to the waiting room, timing it to arrive with only 2 people left in front of me, only waited five minutes or so, had my blood test and went home