Choose time format (12-hour vs 24-hour)

I live somewhere where 24-hour time format is used and it's not intuitive for me to use the 12-hour time format at all. I'd like a preference setting where I can change it. I think it would probably be best to offer a choice between "auto ", "12-hour" and "24-hour", where "auto" would be the default option and uses the format of the user's locale.