Nope, I don't, and in that case 100% of the drivers, over 3 years, have gone the wrong way, because I don't have a car. Yes, I know, I'm an exception in a country with 400K residents and 320k cars . From St Julian's, near Paceville, in my case, which is easier being close to the junction- you can easily take the bypass. Then, after a while you got stuck in mini-traffic jams and then again when you get closer to the airport. The situations has been even worse for months because of the works on Santa Lucija, or whatever is its name, and then the detour. There're a number of roads, but most of them go through small towns and are subject to sudden traffic jams.
If everything is fine, you can manage to get to the airport in 20', as Jdiver pointed out - which is an appalling timing anyway, in my opinion, for such a short trip - otherwise, it takes longer.

Well, 'only' 50', for a bunch of KMs,... Anyway, Xemxija, it's a different story. The main 'backstreets' are usually not subject to traffic jams. So, usually, you don't have problems, around Xemxija; you may encounter some issue when getting closer to the airport.
Distance doesn't really matter. Traffic is the issue, or even better the lack of something we may call 'roads' plus a Maltese fad: cars, cars galore.