Did ten years with SQ on the B744. Never had a problem with ATC starting 1,2,3 & 4 individually, especially if they let you start up to two engines on the push. Procedure can be accelerated a bit by initiating start on next engine when preceding one becomes self sustaining, EGT backing off, rather than waiting until fully stabilised. Even starting all four individually and letting each one stabilise you are talking less than five minutes and in my day both FRA and LHR would usually let you start on the push, surrounds permitting.