Forever, I guess. I remember having them when I was a kid. When Maeve was little, I had a dream that she fell out of a tree and got hurt really bad. The next day, she fell and I mostly caught her so she just got a sprain. That was the first time I knew they weren't just dreams.
Depends on how often I actually sleep. But when I close my eyes, I rarely just dream anymore. It's Ronan or it's...everyone else.