Create a list of time in M:S, each value must be repeated 3 times

I’ll use strings for the times in the list because I don’t know which data type you hope to use for them. I’ll also use a 24 hour clock.
Hope this helps:

[f"{m//3}:{s//3:02d}" for m in range(24*3) for s in range(60*3)]

This will only work if you are using python 3.6 or above, because that’s when f-strings were added. If you’re using a version below 3.6, you can use .format() instead, replacing every instance of f'{x}...{y:02d}' in the code with '{}...{:02d}'.format(x, y).

Edit: Modifications of int(x/3) to x//3 and replacement of secs logic to :02d based on @MadPhysict’s recommendation.