This morning I put together some firmware to carry out diagnostics on the boards. When uploaded to the microcontroller the firware checks for the presence of the SD card, config files and then verifies that timestamps written to the RTC are stored and read correctly without error.
Naturally, this was developed on a board which fails all tests. #UnitTesting. Kinda. The next stage is to upload this to the boards and find out what the current situation is.
You may have noticed the sensor remains unchecked. This is because at the moment I don’t have access to a signal generator to produce fake signals. Rest assured, as soon as I’m back in the lab that test will be written.
Dan Mannion - Electronic Engineer 
Turns out RTC is working on all board good news. SD card is destined to fail as they are all locked away in the office. Not too worried about the SD card tbh moresoe the actaul sensor boards. They appear to have corroded with exposure to teh volatile acids in the test chambers.