For a one-shot, pre-gens are definitely your friends. By all means ask the players what they'd like to play, but once that's done create the characters yourself. And tie those characters into the adventure you're running, so that there's no question of why they're doing what they're doing - it's on the sheet.
Secondly, as others have said, everything will take longer than you expect. So, if you think you can get through five encounters in five hours, that means you can actually get through three.
(Unfortunately, 5e is a bit of a different beast from 3e and 4e, so doing that estimation may be difficult.)
Keep the characters low-level, but not so low-level that they'll die instantly with one critical hit. In general, I would recommend 3rd of 4th level - somewhere near the top end of that "low level" tier. That gives them a bit of sticking power, and gives some variety of powers, but it doesn't bog down the game with lots of minutae.
I disagree about not including mysteries, and discoveries, and the like. Bear in mind that the game has three pillars, and try to include
something for all three. That said, avoid any
necessary discoveries - try to set things up so that if the players solve The Riddle of the Sphinx then they get some cool easter egg; but if they don't then they can complete the adventure nonetheless.
Finally, take a look at the free preview for
Weird Discoveries, and use that as a basis for your preparation - a central map (or node diagram) with appropriate bullet-point notes for what may happen in particular areas.
Have fun!