In most people's experience these days, computers produce answers and generally do stuff almost instantaneously. But those who program computers to perform complicated data analysis and simulation tasks know that they can sometimes take hours or even days to complete a calculation. This of course depends on the sheer volume of number-crunching required.
In a game context, what dictates the amount of time needed for a computer calculation can be dramatic necessity. Need to crack a pass code to gain access to the safe of an evil corporation? How long will it take? It's tricky to say in any realistic way how long such a calculation might take, especially given all the variables, including but not limited to the fact that the computing technology being used probably doesn't match any present day, real world computer.
Let's see then... if the guards will arrive in about five minutes... the computation will take about five minutes...
Leia: Let me point out the flaws in your plan.
Leia: Firstly, who is going to assassinate Darth Vader? Secondly, how is anyone even going to get to the Moon without being blown out of the sky? And last but not least, Luke here is too chicken-livered to use the damn Force!
R2-D2: Your plan has that second flaw too.
Leia: Yeah, but that's still two flaws my plan doesn't have.
R2-D2: Look, when I was in there I installed a back door.
Chewbacca: Not the most awesome rate of success with that one, old chap.
C-3PO: Artoo, since you know everything about the Moon, you can figure out how our fighters can fly to dodge their guns.
R2-D2: Right! My plan has no flaws that cannot be solved. I'm on it.
GM: This is the most complicated vector optimisation problem you've ever had to solve. It'll be a tough roll.
R2-D2: Okay. Shutting down all external systems. Full processing power. Sorry guys, I'm out of this conversation for a while.
C-3PO: Oh dear.