Heathrow Express left Paddington at 0941 and arrived at the airport at 0955. Even with 13 minutes walking time to the check-in counters I was early for my 1030 checkin. What is the latest Heathrow Express I could take to be not late for my 1030 checkin?
By 1020 I was through security screening. But it is another 15-minute walk to the gate. Boarding is at 1130. What is the latest time my Heathrow Express should leave Paddington for me to be at the boarding gate at 1130.