manual frustration with the E-M5!
Whatever I do I can't get the bulb function to work and see the resultant image happening in the viewfinder or LCD screen.
This is called 'Live Bulb' or 'Live Time' and you have to enable it in the setup menu. The number of refresh is limited, but you will see the image evolve at fixed intervals during a bulb exposure.
This only works in BULB or TIME mode, in case it is not obvious which seems the case from your comment. To do that, you have to set the time past 60" to when it says TIME or BULB. At that point you are in BULB mode and press the shutter to start the exposure and either hold it (For TIME) or press it at the end (For BULB).
Setting up the Live Bulb and Live time:
Note: In order to use either function, you must put the camera in Manual Mode (M) and scroll the main dial until you see the option. Rotate shutter speed dial until way over 1 minute since those options are beyond that time threshold.