Apple Watch series 3 and can not get it to display 24 hour clock... iOS 11.3.1

Have you turned on 24 hour mode on the watch, or just on the iPhone? If you wish to see 24 hour time on the Apple Watch, then on the iPhone go to the Watch app, then tap on My Watch>Clock and turn on the 24-Hour Time switch.

I've not experienced any problems with mine in 24-hour time. Although I also have my iPhone in 24-hour time. So you have powered the watch off and back on and no change? I'd suggest powering the phone off and then power the Watch off. Turn the phone back on and then the Watch. Let them connect again and see if that helps. I would try that before having to unpair the watch from the phone and pairing again. That can take a bit of time.

to change to military time on the apple watch go to your iPHONE. open the apple watch app. select CLOCK. at the top slide over 24-HOUR TIME.

Okay, I use the modular face, but I have seen others. Guess that would be something you would need to test. I know that none of the analog faces would not. I believe if you go to the Watch app on the phone, and check out the different faces, many will display what features they have. Glad you were able to sort this out.

What happens when you try it? What other troubleshooting have you tried?