Why shouldn't I ask my users to enter times using military format

Question

I have a form that asks users to enter a start and end time for an event. For many years, we have allowed them to enter the times by selecting the hour (1-12), minute (1-60), and AM/PM from three drop down boxes. This has worked fine without complaints from customers. However, today I was hit with a request to change the input to one text box for the user to enter time in military time (aka 0000 - 2359). In my gut I believe this is a bad idea but am having trouble coming up with any hard facts.

What are the best reasons I can give that this would be a bad idea?

If there is a better solution for entering time, what would it be?

Also, FYI the users filling out the form run the gamut from very little skill with computers to advanced users. They are in no way military related.

Update: All my users are local and no other forms (web or print) use military time as the standard.

Answer 1

Three dropdowns are a nightmare usability-wise. You can cut these down to two by eliminating AM/PM and moving to 24-hour format, but still: a dropdown with 60 items is overkill.

I'd much prefer to enter time "manually", provided that these input boxes will be intelligent enough (say, they should be able to convert 18 to 1800, 0 to 0000, allow : as a separator, etc.). Plus do not allow users to enter incorrect data in the first place.

To answer your question: I see no reason to disallow your users to do what they want. After all, they are users.

Answer 2

Well, from a user interface standpoint, this could be a mistake simply according to some of Jakob Nielsen's user interface heuristics:

"Match between system and real world." If your users are not used to entering dates in military time, asking them to do so for your app can be distracting at best, and frustrating at worst.

"Error prevention" You are not eliminating error-prone conditions, but possibly introducing them.

There is also the question of why this change is being made. Are customers complaining? Is data coming in incorrectly? As mentioned by others, are your users used to military time? Any interface change should happen for a reason, IMO, because you're going to change the user experience and there will be ramifications for that; it's just a matter of how large those ramifications will be. My assumption is that data entry errors are supposedly going to be avoided -- but are they? Asking a user to enter a time as "XX:XX" and parsing out the semicolon (or, as Aaron Digulla stated, ANY non-number characters) and then converting it as needed seems less likely to result in errors than asking a user to enter a time in a format they are not used to using daily.

My concern would be that a user wants to enter 3:30 PM, and, while not paying much attention, simply enters 330. This is now 3:30 AM, and the user will never know the difference, because the app takes the information and happily assumes that this is what is meant. However, allowing the user to enter the time in "XX:XX" format and having an "AM/PM" selection makes much more sense.

As far as hard facts, well, I don't have them either. But if your boss/client won't be swayed by Nielsen's heuristics, I'm not sure what can change their mind.