I'm sorry Grum but that is completely incorrect.
At DXB Medium A/C are given the standard ICAO departure vortex wake spacing of 2 minutes behind a Heavy and 3 minutes behind a Super departing from the same point, this is increased to 3 and 4 minutes respectively should an intermediate departure point be used. The time is measured from the moment at which the previous departure rotates and the Controller will factor in the time it takes the following Medium departure to rotate when giving the Take-Off clearance.
The OP's original question related to Heavy following Heavy and at DXB this changes slightly depending on weather conditions. When using Reduce Rwy Separation (RRSM) the first A/C must be at least 2500m down the Rwy and airborne. When RRSM is not able to be used it's one minute which is roughly Rwy length and in either case the second A/C is not transferred to Radar until 4nm separation is achieved. These times and spacings are minimums and will increase if consecutive departures are on same Sid's etc.
Grum, if you require greater than the standard ICAO spacing that we provide at DXB just ask for it before lining up and you will probably depart behind the next medium departure.