Using noise isolating headphones poses no additional risks beyond regular headphones. Using high quality headphones poses no additional risks beyond wearing hearing aids, and in fact the materials are often the same. The risk of prolonged listening is overall exposure. There are a who bunch of standards for calculating the overall noise exposure dose. This a a nice online calculator.
There is no standard that makes use of breaks. The goal of the standards is to limit your total exposure. As an example, with OSHA, you can be exposed to 90 dBA for 8 hours and 79 dBA for 16 hours. It doesn't care you the 90 dBA period is divided. In other words, OSHA does not care if you take breaks.
That said, there is not a strong evidence base supporting the standards. As I said in this answer of mine, hidden hearing loss is an active area of research. The focus of the research is predominately on non-maximal noise doses. I am not aware of any research looking at the effects of breaks on maximal, or non-maximal, noise doses.
As i said in my other answer, What is known is that there is no way to reverse hearing loss. There is no pill you can take. While hearing aids do restore some level of hearing, you should take care of your ears. If possible, you should stay well below a maximal noise dose.
If you listen to your music at 80 dBA for 16 hours a day with 8 hours of quite at night, that is a 50% noise dose based on OSHA. This is the action level, where an employer would be forced to institute a hearing conservation program. You should attempt to stay even further below this.
