Stator,
We were no 3 for 15R, RYR 7764 was the aircraft in question, taking off on 15R immediately behind an A-340, also on 15R. A pilot gave the 'warning'. ATC said "ok' or words to that effect.
Heathrow Director,
Does your timing start from take off roll or rotation point? I've never heard of the later being a criteria. I do, however, always witness aircraft releasing brakes at the 2 min point in the UK...... (not that wake turbulence knows which nation it is about to bite!!)