The previous comment was just copied and pasted ahh! but I have a lot of experience, I use dream radar all the time.
Things that you should know:-
It's actually 23 hours and 59 minutes and not 20 hours.
Change dates or times on your ds (this adds a 48 hour penalty of going back to Pokemon dream world. So don't do this unless you want to be barred for 48 hours due to setting issues.
Only one Pokemon may be taken out be every log in e.g. every 23.59 hours.
You must grow berries otherwise you cannot progress further into the game.