Since LHR has been mentioned and for the benefit of the OP, this from mLido LHR procedures:
Minimum Runway Occupancy Time (MROT)
Ensure standard MROT procedures and in addition:
When receiving a conditional line-up CLR on a preceding DEP ACFT, remain behind the subject ACFT but
may cross RWY HLDG point (subject to there being no illuminated red stop bar) and enter RWY upon
receipt CLR. There is no requirement for the subject ACFT to have commenced its TKOF roll before
entering RWY. Be aware of the blast hazard.
(apologies for the formatting).