In the US you can definitely say 17:00, but we would say "seventeen-hundred hours". It's similar to how we communicate four-digit street addresses, so 17:05 is

In the US you can definitely say 17:00, but we would say "seventeen-hundred hours". It's similar to how we communicate four-digit street addresses, so 17:05 is "seventeen oh five" with or without "hours" at the end. I picked it up from military people I think. I don't do it unless the other party uses 24-hour time though. I wish everyone did because people often omit AM/PM and then you have to ask for clarification, where as "eighteen-hundred" is always obviously 6PM and can't be confused with 6AM.