You're "in the zone" all the time your track takes you inside the lines on the chart.
Again, helicopters are put on the published routes so that the IFR traffic can be ensured the normal IFR separation from all traffic inside Class A airspace. Radar controllers understandably get concerned if a helicopter strays off the allocated route by more than a few metres and will correct the pilot. When LHR is using the easterly runways, some heli-routes (e.g. H3) are closed in order to ensure continued separation.
Helicopters under SVFR are allowed to pass each other along certain routes, such as those following a line feature like the Thames, if both pilots agree.