It depends on the depth and breadth of the project, how many other people are involved, and how many other projects are going on at the same time. (I had a boss once that would hand out major projects like they were candy, then say "why don't you have that done yet? You've had it for 3 weeks", as if that was the only project I had to work on).
One of my favorite phrases (stolen from the quality control guys) is "Nine women cannot make a baby in one month" - sometimes things just take time.
It's not just bosses that don't understand about things taking time - it can be clients too. If they really understood what it takes to complete the projects, then they'd be doing it themselves. One thing I do for my clients that seems to help is I spell out every sub-task and sub-sub task when giving them the quote or at the start of a new project. It helps me figure out what I need to do and how much I need to charge, and it helps my client understand what it takes to complete what they're asking. Don't know if that would help with your client, as some bosses could care less, they just want the job done. But you could always try!
hth
