Yes indeed. It does take an hour or two to a whole day.
I'm in the mindset that when you go off on adventures by yourself, its pretty selfish, because you're taking away an experience (and XP) that could've been shared by a group (You actually get less xp by soloing, so it's also counter productive). I realize soloing is a preferable alternative for some, since sometimes groups are clunky, and not everyone works well with everyone else, but keep in mind that these areas are designed for groups, and usually when you are soloing, you are soloing areas designed for groups of multiple levels lower than you.
On the plus side, for ninja looter people, I recently learned that ninja looting is a victimless "crime", since the loot returns at its fullest spawn as long as the monsters in the area are kept at high spawn, so this method of soloing has my full endorsement. The only way it hurts anyone is if a group goes in within a half hour to an hour after your sweep, which is pretty unlikely unless its a place very close to Vallaki.