we would arrive only to either land before the night jet ban at LHR (landing before 0602 local) or have to take up the hold until after 0602 local
There isn't actually a "night jet ban" at Heathrow. I suspect you're thinking of the night quota, which limits the number of movements before 0600.
So, for example, CPA251 is allowed to land before 6am, but under normal circumstances CPA255 has to hold if it's early.