My guess is it depends. I don't think mine ever did.

When they are hard, they stay that way until I orgasm.

Mine got puffy right around when I started puberty (hair growth), and stayed that way for a month maybe? I was scared and thought I was growing tits, but found out pretty quick that it is all part of puberty and the hormone surge that happens right when you start.

For most boys I don't think it lasts very long. Mine never got puffy but my brother and some friends went through it.

mine are starting to do that but they are sensitive