As you can see the two time stamps are 8:18 and 8:28. You can assume from "before I went to work" that I didn't check after the second one (8:28) as I was on my way to work, and it's also a safe bet that the first one (8:18) is when I first tried to get on it. So using your head and safe bets you'd know it was 10 minutes atleast. Unfortunately I can't give you a better idea than that. TLDR, 10 mins minimum, might have been longer. I know there's a 30 min downtime, when is that UK time?