Use separate textboxes for the hour and minute values and a pair of radio buttons for AM/PM value.

Typing desired values is usually easier (quicker) than clicking or pressing a button to get to them. Just think about the worst-case scenarios for the number ranges you're using.

For a 12-hour clock, the greatest distance is 6 if you can go from 12 to 1 and vice versa; for minutes in an hour, the greatest distance is 30 if you can go from 59 to 00 and vice versa.

So, let's assume the default is 12:00 and I want to input 6:30. I have to press the Increase Hours button 6 times and the Increase Minutes button 30 times. That's a max total of 36 mouse clicks not including possible clicks for AM/PM selection and form submission.

I could hold down these buttons for indeterminate amounts of seconds, but that's part of the problem: it's hard to predict ahead of time how much to hold.

In contrast, if I'm able to type and I want 6:30, I just go:

6, Tab, 3, 0

Use separate textboxes for the hour and minute values and a pair of radio buttons for AM/PM value.

Typing desired values is usually easier (quicker) than clicking or pressing a button to get to them. Just think about the worst-case scenarios for the number ranges you're using.

For a 12-hour clock, the greatest distance is 6 if you can go directly from 12 to 1 and vice versa; for minutes in an hour, the greatest distance is 30 if you can go directly from 59 to 00 and vice versa.

So, let's assume the default is 12:00 and I want to input 6:30. I have to press the Increase Hours button 6 times and the Increase Minutes button 30 times. That's a max total of 36 mouse clicks not including possible clicks for AM/PM selection and form submission.

I could hold down these buttons for indeterminate amounts of seconds, but that's part of the problem: it's hard to predict ahead of time how much to hold.

In contrast, if I'm able to type and I want 6:30, I just go:

6, Tab, 3, 0

Use separate textboxes for the hour and minute values and a pair of radio buttons for AM/PM value.

Typing desired values is usually easier (quicker) than clicking or pressing a button to get to them. Just think about the worst-case scenarios for the number ranges you're using.

For a 12-hour clock, the greatest distance is 6 if you can go from 12 to 1 and vice versa; for a minutes in an hour, the greatest distance is 30 if you can go from 59 to 00 and vice versa.

So, let's assume the default is 12:00 and I want to input 6:30. I have to press the Increase Hours button 6 times and the Increase Minutes button 30 times. That's a max total of 36 mouse clicks not including possible clicks for AM/PM selection and form submission.

I could hold down these buttons for indeterminate amounts of seconds, but that's part of the problem: it's hard to predict ahead of time how much to hold.

If I want 6:30, I just go:  6, Tab, 3, 0

Use separate textboxes for the hour and minute values and a pair of radio buttons for AM/PM value.

Typing desired values is usually easier (quicker) than clicking or pressing a button to get to them. Just think about the worst-case scenarios for the number ranges you're using.

For a 12-hour clock, the greatest distance is 6 if you can go from 12 to 1 and vice versa; for minutes in an hour, the greatest distance is 30 if you can go from 59 to 00 and vice versa.

So, let's assume the default is 12:00 and I want to input 6:30. I have to press the Increase Hours button 6 times and the Increase Minutes button 30 times. That's a max total of 36 mouse clicks not including possible clicks for AM/PM selection and form submission.

I could hold down these buttons for indeterminate amounts of seconds, but that's part of the problem: it's hard to predict ahead of time how much to hold.

In contrast, if I'm able to type and I want 6:30, I just go: 

6, Tab, 3, 0