This is exactly how people perceive execution time. If a progress bar goes to completion and then hangs users will perceive that operation as taking longer than if a progress bar goes to, say, 70% and then jumps to completion, even if the total time of the operation is the same.
It makes sense though, people are the most impatient when they've been waiting the longest so being surprised that the operation completed faster than they were led to think it would is more welcome than having to wait longer than they thought they'd have to.
It makes sense though, people are the most impatient when they've been waiting the longest so being surprised that the operation completed faster than they were led to think it would is more welcome than having to wait longer than they thought they'd have to.