The point of all this isn't to estimate exactly how fast it will take to do a task. It's to compare how efficient one way is against another.
Newer, faster computer will do them faster. A DDOS or CPU overheating will slow them down. But that's not the point.
Lets try a crap example I just made up. Imagine you want to go with your friends to see a movie. Here's a bad way to organise that. You drive to your first friends house. Ask what they want to see. Then you drive to each of your other friends houses and tell them what friend 1 wants to see. Then you drive to friend 2's house and ask them. And then drive to each of your friends houses (including friend 1) to tell them all what friend 2 has.
Can you see how with a large group of friends, that would be insane? It really doesn't matter if you have a fast or a slow car. It's just crazy.
A better plan would be to drive to each friends house, ask what they want to see and write it down on a piece of paper. Then at the end -- you can drive around again and tell everyone what movie you are all going to see.
If you've got 2 friends -- in the first plan you get to visit 4 houses. And in the second plan you get to visit 4 houses. With 3 friends it's 9 and 6. And then 16 and 8. And 25 and 10. 100 and 20.
Now lets say the person doing plan 1 discovers this amazing thing called the telephone. Plan 2 person is still using a car. Person 1 can do things so much faster. They don't have to leave home and can call in a manner of seconds.
But let's think it through.
4 calls vs driving to 4 people. 25 calls vs driving to 10 people. Still a big win for plan 1 at the moment. But how about 10,000 calls vs 200 car trips? 1,000,000 calls vs 2,000 car trips?