When I burn CDs to iTunes, they don't appear in my library straight away and sometimes not at all?

Just wondering if anyone else has the same problem?

I import songs, and when I type them in the search bar (in library) they appear but then they don't play, as they are not in the library. But if I try to burn the cd again it says its already been imported???! Sometimes they appear in my library at a later date but I don't understand why it's taking so long??