Warning Ahead of Time
Since your definition of short ("5-7 hours") is longer that what most people describe as normal (3-4 hours), this advice may be a bit off, as it's for truly short sessions (1-2 hours)...
Systems with streamlined, unified mechanics
You want a system where the mechanic is almost always the same kind of rolling, where the combat system resolves in a roll or two per player, and where few, if any, in play lookups are needed.
Since you're already using WW's engine...
You can easily drop the combat system from Storyteller for a set of opposed rolls. We can borrow from Burning Wheel a bit...
Each side states a "goal" for the combat - the side that gets more successes gets their goal. Each success also becomes a damage level done or canceled; The winning side does the difference in damage levels and takes 1 damage level per 1 rolled; the loser does damage levels only for 10's rolled. Each such level is applied to one target. No matter what, the combat scene is over after the one roll.
Mission Based Play
To be blunt: Play with obligated characters - that is, characters who can't say "no" to the current adventure. Dresden's notorious lack of cash can force him into adventures. Karin Murphy HAS to investigate (at least for 12 novels) supernatural involved major cases. Donald Morgan has to investigate certain crimes, too; as the Warden, he's got more leeway than Karin, but really, he's just as dutybound. The Thomas Raiths, Chastity Carpenters, and even most of the Fae really don't have that - they have enough freedom to just say no. Molly becomes obligated when Harry takes her as apprentice.
When it droops, kick it
Don't let play lag. If they start to drag into a discussion that's not getting somewhere fast, give them a warning to pick a plan, and if not, drop a "kicker" on them. This could be something as innocuous as Toot's arrival in several of the later novels, or as big as Nicodemus dropping in for some quality time. Nothing makes a story feel less like it's making progress than a long debate over which way to go.
A requisite of this is that, if the players are discussing plans, so are the characters, for the same amount of time, or more.
If they don't have a clue, give them one
When things slow down because they don't know where to look, it's your fault as the GM. It means you haven't given them enough information. Cure it. Use an NPC, a familiar or a book. Give them the pointers in pairs, and let them pick which first, if you want to give the sense of choice.
When they search, they always find
To borrow some advice from several good games, including Burning Wheel... a failed roll isn't always a failed attempt; sometimes it's a success with a complication.
Harry tries to find the big bad with a spell. It works. It blows up his lab on that fail, but still finds the big bad.
Thomas tries to Track down Harry - he does, but not until Harry's being hauled by the big-bads.
Don't make the minions too tough
It's easier to add more than to soften them up on the fly. But if you have a plan, and realize it's too tough, after the PC's dispose of the guys who already had a bunch of unexplained damage levels, when they round the corner, the PC's find the other set of people who just fought them first... dead and/or dying.