In response to your questions.

I only moved the time and date around in response to Dick suggesting I go back to before the DST to UTC time change and run sky flats again which I did. The flats for the artificial 26 October worked fine second time round with PC clock changed. On the real 26 and 28 October Sky flats worked correctly.

I only changed the time on the PC. When ACP connects to the scope it automatically loads the date and time into the mount and this is confirmed visually on the hand controller. The PC and mount have the same time and date.

Sky flats were the first thing done after scope connection and time and date updated by the PC to the scope. I do not know what you mean by observing fixing time/date/lat/long. These are set on startup, why would observing change them?