If it's the first flight out they are likely to board and perhaps leave a little early .. but even still arriving at LCY 45 minutes before scheduled departure I'd be totally comfortable with , especially with the new security where you can leave everything in the bag ... If you've got to check a bag in add a few minutes on .. but you really don't need much more .. the place is tiny ( and with all the construction going on airside there's very little to do other than board the aircraft after security )