You have to
wake up to send it to Entree Forest. And when you wake up you can't go back to the DW til the next day (after 24hrs).
The best way to be able to go multiple times to the Dream Island is to befriend w/e pokemon you want, gather as many berries as you can find, and when you get to the Tree of Dreams, DON'T make a wish, just go back home and go back into the Dream Island a few more times. When it's run dry of any new pokemon/items, make your way to the Tree of Dreams and make a wish for a pokemon that you befriended during that hour (or previous day if you didn't make a wish for a pokemon the day before cuz they'll still be listed).
After all that is said and done, either water your berries, or make the rounds at other random dream user's gardens/share shelves. After all that, you are pretty much left with nothing else to do but leave the Dream World if your hour isn't up yet.
Further Reading.
Bookmarks