There are a few different date and time formats followed around the world, and there is the ISO format. The ISO format has done much of our thinking for us so if you need to consider various date and time formats you might as well just pick the ISO-recommended approach and be done with it. But if you should need something more bespoke, the following are some ways of thinking about this deceptively simple consideration.

The local format

Why not just follow the format most populat in your country or region? We will not pretend that the date 9 July would confuse something because it was written as 7-9 instead of 9-7 although this can be a very real concern. Assuming you can go past that somehow, the problem with local formats will simply be that more than one group of people can be misled by it especially when collaborating. If you do not have a proper standard in place, how we format the date is not something we think about. So even if you do insist on using your local format, explicitly standardise it for your project.

However, unless your local format adheres to our recommended format (which we will discuss presently) you might not want to settle on it just yet.

Decide on the granularity

You do not always need the date and time down to the seconds, and yet plenty of software will default to this leaving you with a clumsy date and time stamp that looks unique and mysterious but is really pointless. It can be useful if you are making incredibly brief zettelkasten notes at the rate of three a minute (which is doable but one wonders why) because then you will have three notes made in one minute and the seconds become the sole unique identifiers.

In a more realistic scenario, though, consider how often you do make notes in that category that are worth thinking about in terms of temporal differences. And keep in mind that notes have file names too that makes them unique. The date stamps are only part of the picture and need not carry the entire burden of uniqueness and identity.

So ask yourself pertinent questions. Do you just need the year and month? Is this a daily note so you need the year, month and date? Or is this something you associate with work meetings so you need to go all the way to the hour and/or minute?

There is only one true sorter

Alphabetic ordering is the most commonly used ordering after ordering by modification date. This helps when you know roughly what the file was called and having things sorted by alphabets makes it easier to scan. Likewise alphanumeric sorting is great if you might know when you had a meeting – say on 9 July 2025 – and you want to quickly get to that file without much hassle.

Consider how your computer sorts date-laden file names alphanumerically for files bearing the dates 9 July 2024, 11 June 2025 and 5 August 2025.

05_08_2025--meeting_3.md
09_07_2024--meeting_1.md
11_06_2025--meeting_2.md

This is not exactly useful because, while the dates contain all the information you need, they are sorted senselessly. The same is true of the American month-date-year scheme although this does ever so slightly better by correctly sorting within a month but across years:

06_11_2025--meeting_2.md
07_09_2024--meeting_1.md
08_05_2025--meeting_3.md

The only useful answer should be obvious by now: order the date from the largest time span to the smallest going year to month to date and so on:

2024_07_09--meeting_1.md
2025_06_11--meeting_2.md
2025_08_05--meeting_3.md

Note that we are following here the pattern of underscores and hyphens previously mentioned in our discussion of file naming schemes.

So there is, it turns out, an indubitable ideal format to date and time stamps viz. yyyy MM dd and HH mm ss all with leading zeroes for clarity and in that specific order. The niche case when this fails is if, for some reason, you work exclusively on month-to-year or day-to-month/year basis, in which case you would want to sort, for example, across all Julys between 2010 and 2023. This is highly unlikely to be a common scenario and is nevertheless not worth deciding your entire file naming scheme on just because of all the other downsides it brings.

Finally, none of this means you should use these date formats in the body of your document. These are just for tables and file names and wherever they may become instrumental to sorting your files and helping you scan through your directory structure.