You can get the date from your journals in
%USERPROFILE%\Saved Games\Frontier Developments\Elite Dangerous\
, just search all .log file contents for "Sagittarius A*", it's simple text files. The line containing the string
"event":"Scan", "ScanType":"AutoScan", "BodyName":"Sagittarius A*"
should show when you scanned the supermassive black hole I guess. There's a timestamp in that line too.
I'm also missing something though. I didn't know about this thread when I went there, so I didn't think of including my Commander's name in the screenshots

. I can provide the visitor's list link through: [
Here's my visit].
CMDR Azar Javed - 12th June 3305

My visit in SagA*
(click to enlarge)