This is a simple datapack that adds a 12 hour/24 hour time measuring system to your Minecraft world.
...
Yeah...
That's all it does.

You get a nice little tracker above your hotbar that shows the current time.
You can change the time measuring system with the /function timetracker:settings/12hour and /function timetracker:settings/24hour commands.

New! Users can now set a colour theme for the tracker. This doesn't require operator permissions, and can be set to any of the six below themes with /trigger time[​Theme]:

• Blue (The default)
  
• Green
• Red
• Purple
• Yellow
• Mono (Grey theme)

If you're interested, this is every function in the datapack, although you usually only need to use the setting functions:

• timetracker:init - Loads up everything to make sure it works. Automatically runs when the world loads or /reload is used.
  
• timetracker:remove - Deletes the scoreboards created. Just in case you need it.
  
• timetracker:maths - Does all the math stuff to get the correct time. Constantly runs.
  
• timetracker:display - Runs the code to show the actionbar message. Constantly runs.
  
• timetracker:colours - Manages individual colour settings. Constantly runs.
• timetracker:settings/24hour - Sets a scoreboard value to 0, to disable 12-hour time.
  
• timetracker:settings/12hour - Sets a scoreboard value to 1, to enable 12-hour time.
  

Okay, that should be all. Feel free to modify this for your map or server, as long as you attribute me for creating it. if you do actually use it, please let me know! It'd be cool to see how it's being used.