There is a maximum time limit on modifying your posts.
Ok, I see now. I'm not quite sure why this is so (maybe about server issues :/ ) but I'm not going to complain
The thing is, I've provided a link in a post for a GM who actually didn't want it to be too obvious.
I wanted to delete the link the following day, but obviously couldn't.
But that's ok, the guy said he'll manage the issue. No big deal in the end.
Thanks for the answers anyway