This looks like a bug, and is likely a bug in some localization (the autocorrect entries are part of localization).
Back in 2016, when version 5.0 was released, where emoji support was introduced, we had an implementation error tdf#97191, that was treating the sequence colon-number-colon as a clock face emoji (like
🕐). But since that clashes with normal way of entering times, those entries were changed to strings like
:1 h: since version 5.2.2. And the localizations followed (e.g., in Russian, it now accepts
If you had that in 188.8.131.52, it could mean that some localization had that wrong in that version, and that localization was active for your input (a cell having that language set?) - I cannot test that myself at the moment. In that case, I’d expect a bug report on that, and also to be fixed immediately, in the next release (I don’t believe that that kind of problem could go unnoticed for long) - please try version 6.2.5.
Or the incorrect entries could somehow appear in the settings (user entered them? a leftover from upgraded version 5.x?).
Please try to locate which autocorrect has the problem: your locale (see LibreOffice language settings to see which is active in the program - you said that’s en_US)? your document language? a cell style language? Locating the wrong entries may help you to fix that by removing them, and also to file a bug if that turns out a localization issue (not a leftover frm an older installation).
Note that while you are entering anything into a cell, it is text yet - until you have finished entering, e.g. by pressing Enter in Calc; only at that point it tries to recognize the input (takes the entered string, and tries to interpret it as a number, or a date, or a percent, or currency, etc.) - so it’s incorrect to apply the date/time internal representation (as a floating-point serial number in Calc) considerations to the process of input (before the input was finished), where anything is still text. You can see that the autocorrect happens while you are entering, not after you hit enter.
Also date acceptance patterns has nothing to do here, for the same reason.