Minecraft timer?

I want to do a speedrun with friends in Minecraft, but I need a timer in Minecraft Vanilla. I tried to solve it with scoreboards, but unfortunately I failed. Now I ask here and hope that someone can help me.

Just watch the video here at MFG.

Thanks for the answer, but I don't want to download anything. I want to display it integrated in Minecraft in the actionbar or in the bossbar

1. Create scoreboard timer with value 0 and scoreboard one with value 1. Create scoreboard trig with value 0.

2. Redstone clock for one second:

Check whether scoreboard is trig 1.

Add scoreboard timer with scoreboard time.

If trig is 0 then set it to 0.

4. Set trig to one for start with command block and zero for end.

And then synchronize with bossbar every time. Goes by command. Google this easy.

You create a scoreboard, for example "timer":

/ scoreboard objectives add timer dummy

Then add the fake player "timer" to the scoreboard "timer":

/ scoreboard players add timer timer 0

Then you build the following for example underground:

The command must be in the command block

Each repeater is at level 2 so that the command block is executed every second.

For example, if you power a repeater with a lever, you must turn the lever off immediately afterwards. Then the timer runs!

But then you have to see if that works in the nether and in the end.

You can of course change the name of the fake player and the scoreboard.