There are a lot of ways to find numbers that are "first on the moon", so this question may need some more specificity to rule out answers; right now there doesn't seem to be any criteria beyond "the largest" number an answerer might justify somehow, which is probably too broad.
It's possible the password is
We know that
OP uses passwords that are usually pretty long, as we learned in Unlock My Phone! January 2018.
We're looking for the largest "first on the moon" number.
China recently made the first landing ever on the far side of the moon - the robotic
Chang'e 4 mission touched down in the Von Kármán Crater at 10:26am Jan. 3, Beijing time.
This is clearly a "first" on the moon, both for China (first moon landing at all) and for humanity (first landing on the dark side of the moon).
If we take the date and time, in GMT, of this moon landing, we get 201901030226. Seconds were not given, so this is the most specific timedate stamp we can get.
Since this is the most recent moon landing, if we were to consider any other "first" - by nation, by mission type, whatever - and take their corresponding YYYYMMDDHMM number, this one would be the largest.