There are many different types of stretching routines (static, ballistic, etc), and different ways to approach similar stretching routines.
The way that you mentioned is a good way to do it. Many MA people use a similar routine. I do not think there is any risk of damage from the times you mentioned, as long as you do not exceed a safe stretching angle.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin