In the USA, the broadcast starts at like 4:45 PM Eastern Time (so 9:45 PM in the UK). They're going to show the ODLH-Pac match first, so I would think the Wlad fight might begin at like 10:45 PM - 11 PM your time. Of course, I'm not sure if you will be watching HBO and if a different feed (like Setanta, if they're showing the match) may start a little sooner or later.