When a perfectionist contract killer takes out the wrong man he has only a few hours determine what went wrong before the Mob kills him.

These last two loglines you've posted are close, let me bring you into my thought process.

'Contract killer' is two words, 'Hitman' is one word
'Takes out' is two words, 'kills' or 'Assassinates' is one word.

In a logline I would go with one word over two words every time.

However your loglines are getting increasingly better and the idea is great. Good luck.