Good news and bad news!
The good news is that the latest kernel available via rpi-update (4.9.46 at the time of posting) does indeed seem to work better. I’ve been running it on a Pi 2 for 45 mins with no timestamp jumps. 4.9.35 on the same hardware would usually break within 15 minutes.
The bad news is that 4.9.35 is still the most recent packaged kernel, so the piaware sdcard image will need to stick with the old 4.4 kernel for now until a more recent version is packaged.