Some of the timing is out in this episode.
The first 10 minutes remaining before curfew pass in about 30 seconds. So do the next 4 minutes.
Number Six notices that Big Ben strikes the wrong number of times, but fails to pick up on the fact that less than 3 minutes have gone by since it struck quarter to.
There are two bullet marks on Rover after the first shot has been fired at it.
Plot wise, this is one of the most memorable episodes (maybe because it's one of the least confusing ones)
This makes the second time that the romantic entrest is "Number 8".