Hi Adam,
Firstly I just amended you post to show the photo in the text rather than as an attached heic file (which some browsers struggle to display!)
Secondly I am 99% sure that you will need a clock-enabled ML (or MCL) audiomaster in order to show the time on BL3500 – a videomaster may also work but I am not sure.
EDIT: I think early BS2500 (with the two-way IR) had the clock function, but to set and operate it you needed to use a two-way remote such as the BL7000 or BL5000. The two-way BS2500 could be recognised by its IR window being bottom left of the unit below the moving glass doors, as shown below:
Location: Warwickshire, UK
My B&O Icons:
