Times and dates
I'm in the UK - these preferences don't always follow local custom here, but I would argue they probably should.
When writing the time, I like to use the 24 hour clock and write it as HH:MM. I always include the leading zero if there is one. When it is obvious you mean the time, I think it's perfectly acceptable to drop the semicolon, so the time would be HHMM.
When writing the date I have two preferences. The first, and I would use this in everyday scenarios, is DD/MM/YY. So today would be 30/11/25. When using my programs on my computer, I like to have the date in the format YYYY-MM-DD. This allows for easy sorting. A good example of when this would be useful would be daily notes in Obsidian. I'm also using it as the standard date notation on this blog.