A perfectionist hitman is drafted by two mobsters to assassinate their Don. Twenty nine hours later; he’s struggling to cope with his dying father, seduced into an electric one-night stand, and, in a bizarre twist of fate, seriously wounded. Can he learn the identity of his betrayer before his world comes crashing down?

All of that really interesting middle section ... is superfluous. You've given us you inciting incident (hired to kill a Don), and the action (once betrayed, he fights to uncover the truth behind the betrayal). I think if you want to include that other stuff you need to find a more organic way for it to put it across.
Also, "the world come crashing down" is a little vague - what specifically will happen if he fails to discover (and catch/kill?) the person who betrayed him?

This sounds like a pretty cool movie idea. For a log line, this is a bit long though. The recommended length is one to two sentences.Maybe try and condense this down and make it shorter and tighter :)

Also, why is it a bizarre twist of fate that a hit man who is going after a key mob boss is seriously wounded? I think that could kind of be expected when going up against such a formidable opponent.