Giving Monsters as Many Hit Points as the Plot Requires

I’ve found, as of late, that I simply don’t have time for long encounters. We only have about 2-3 hours a week we’re together, so getting through multiple scenes is essential. There’s no time to spend the whole session whacking away at a pair of wyverns, so I’ve begun ignoring the monster’s HP and killing the monster off once I think it’s time to move on.

An example: the heroes enter a room with three animated statues. They begin attacking. A half-hour into the assault, the players are looking bored, and all I really wanted the heroes to do was discover the secret passageway in the corner of the room. One of the heroes makes an attack, and knocks one of the statues backwards, which I conveniently have fall back into the hidden door, collapsing the weak stonework. Hey, look! The statue is destroyed in the collapsing rubble. Within the next round, the monsters are dispatched by the heroes. As soon as the plot point is figured out, the monsters simply run out of HP.

Is this cheating? Sure, but it doesn’t cheapen my players’ victory, since they aren’t aware I’m doing it. It’s simply advancing the plot.

I’m even lazier in Star Wars. Since most NPCs you encounter are humanoid, I just give them about 10-15 HP, an overall defense of 15 or so, then bump things up or down based on race and type of NPC. A Wookiee bodyguard might have 30 HP and a Defense of 20, whereas the pathetic Nemodian merchant they encounter and decide to dispatch has a Defense of 10 and 5 HP.

How about all of you? Do any of you do this?