At virtually every job I’ve ever had, managers want my tasks done quickly. Yesterday, usually. The faster the better. Sure they pay lip service to making sure that it’s done correctly, but the pressure to do it fast usually outweighs the pressure to do it well.
What happens when you rush a task?
The same thing every time: you do a piss-poor job of it. It’s wrong, buggy, only partially complete, not what the client wants, difficult to use, or doesn’t integrate with a teammate’s work.
So how do you deal with this? Be honest: both with your manager and with yourself. If there are inessential parts of the task, check whether you can cut them out. But if you leave something in, do it fully and to the best of your ability. If you need help, ask. It’s better to deliver quality work and give yourself a learning experience than set false expectations.