I tested with both PR’s, and I had excellent results with the timestamps improving, however I am still unable to get down to the accuracy of the Emlid Reach. Part of it is because the Here+ GPS appears to receive about 2dB less on GPS signals. I haven’t actually gotten a good FIX for the RTKLIB processing yet.
In addition, the new PR uses the internal clock for the timestamps, and that clock drifts slightly from the GPS time. It drifed at a rate of about 145ms per hour. It’s technically a separate issue, but the results were posted here: https://github.com/ArduPilot/ardupilot/pull/8409#issuecomment-443925409