I am looking at booking an international flight from Heathrow that leaves at 12noon. Looking at connections and bearing in mind it will be a Monday morning, then it seems a train to Reading, then the Air/Rail bus to Heathrow may be feasible. I would leave about 7am, and get to Heathrow if everything went on time, between 9 and 10am.
Am I being optimistic that the trains run on time? And is the Air/Rail bus from Reading likely to be held up in traffic?