You are right. I already noticed I had to fiddle with microseconds in order to get the time accurate'sh. At least I learnt something with my code. As for the battery backup - yes, I didn't think of that.
I've already got small 7 segment common anode digits (10 at this stage, so I'll order another 1/2 dozen).
I do realize the multiplexing is out the window now. Again - good practice and I'm learning heaps.