Deadline event

Hi,
Can someone could how can do this? I want to set up an event with a deadline, but without beginning date. I set it as a task but it take lot of space in my calendar since it's something due in 6 months. I just want to be noticed of it couple of days before this date. Is it possible?
I'm not quite sure I understand milestones, but I could'nt add any description and i'm not sure when we will be notice it's coming soon.
Thanks!!