Thank you both, Terry and Skysurfer.
Took me quite a while to get it... 2 hours actually!
@Terry: "Yes I’m wrong. I was thinking of JD and they start at UT 12."
I had skipped that bit because I didn't know what "JD" stands for and hoped / assumed Terry and Skysurfer were merely talking about a mix up in time zones which didn't really have an effect on Terry's previous explanation.
But it did matter verrry much.
I learned it the hard way and therefore will never forget it.
Julian
Day starts at noon - which keeps all the discoveries made during a nightly observing session within the same date.
Whereas the commonly known UT(C) begins at midnight and equals London time - without the political daylight saving in summer. The format can be written in decimal fractions of 24 hours where the date is then prepended followed by a dot.
So Rob took the spectrum at UTC 14:29 pm on January 14th 2018.
30 minutes after midnight on his local Australian January 15 AEST.
Or: UT 2018 January 14.6035 .
Got it. Thank you.
Sorry for interrupting the thread with these trivia. Maybe somebody else reading here had the same question and confusion and my question has helped them, too.