I find it very stressful to arrive late at an airport so am usually the one pushing to leave earlier. This is why I have valued getting to Silver so much, because then I can be early and enjoy the lounge rather than having to wait around the main terminal. I am also usually the one nagging my party to leave the lounge and get down to the gate...

I like to be at LHR two hours before plus a bit of flexibility for delayed travel. In your situation that is borderline. If the NE coach was the only one available I'd almost certainly be OK with booking that and confine myself to silent fretting whenever it slowed for traffic, but at the same time trying to keep in mind HBO helps. However knowing the earlier MB exists I'd want to take that one. The lounges at T3 are so good I'd be delighted to be there early, but if you are Blue and ET (based on being HBO) that won't help you - perhaps you could sell it to your companion as a good opportunity for a relaxed brunch in one of the restaurants as a nice start to the holiday?

That said I am comfortable arriving at LCY with 50 mins to go, but will actively monitor the DLR status in the run-up and be ready to leave earlier if any problems are brewing.