It could just be a major coincidence, however with upgrading to IOS 12 (and running the latest version of GC) - it seems that now, when syncing GC - it write's the current, up to date, 'Heart Rate' data points to Apple Health. Previously, there was the issue of needing to wait until after midnight, to get the previous days data into Apple Health.
On the downside, it seems this is only for the 'Heart Rate' metric. The other metrics that GC is able to write to Apple Health (Active Energy, Flights, Steps, Walking + Running Distance etc) still seem to behave as before.
I'll double check this behavior during this week, to see if this was by design, or just pure luck :)