Around 70% of the time, the BA25 hasn't got airborne within 30 minutes of its scheduled off-gate time, so to call it "quite a punctual flight" is stretching it a bit.
I can't comment on BA's towing performance, but its poor punctuality can't be attributed to late arrival of an inbound flight as the outbound BA25 has usually arrived in the morning from either LAX, JNB or HKG.
Given the wind I would imagine a + or - on a long haul of 30 mins against the avaerage. Then add in the petty SLF squawks that a top airline like to address before the next flight.
Of course I would expect that the departure schedule should make allowances for this to achieve at least an 80% on-time departure unless somebody has sold them an unrealistic gate time slot forcing them to make believe they will vacate at a certain time
