This user with the new firmware was able to record for 2 hours and 51 minutes without overheating. This wasn’t straight recording as the recording still stopped at the 30 minute mark and had to be manually restarted, which this user did several times in a row.
A welcome improvement.
Firmware 3.0 was released on December 18, 2015 and it improved 4K recording time with the vertical grip attached or when using Super 35mm mode, improved picture quality, and improved automatic chromatic aberration correction. You can download these firmware from Sony for your Sony A7r II or Sony A7s II.