Hmmm... Let me guess what you mean by "the database". I have three possibilities.
1) A site you see for example as
http://dmoz.org/Humor
These sites are generated almost instantly from the editor side of the wall.
Please remember that all sites are verified and described by one of us volunteer editors, giving their free time to do so /images/icons/smile.gif It may take more or less time, depending on the category you submitted to. If you put a specific request we can have a look for details.
2) The search-database
Searching inside DMOZ is done by accessing a database, which is rebuilt about once or twice a week. Someties this process is skipped for some time due to works (like its done on the highway, only that we have a single worker only so it may take some more time /images/icons/wink.gif )
3) Google
If you should mean "Why dont I find my site in Google when its listed in DMOZ" please ask those Google guys. They download their DMOZ-copy (which is generated once a week) about once a month or less often. Not our fault and nothing we could change.