I too am in the ‘risk adverse’ camp. However… if I absolutely had to do it in a day, I would want to be on the very first flight from MAN, with a backstop that if that was canceled there would be at least one or two more flights that would get me to LHR in good time.

And Plan B, in case of flight disruptions, would be to have a hard time in the day (probably around 15:00) when I would go ‘I am outta here’ and leave MAN and go and catch the train.