Originally, the “rings” in this story were a trio of bracelets. They were bronze, silver, and gold. One bracelet could send you back in time. Having two bracelets could send you forward–possessing all three granted the ability to travel to any time period.
This presented some logistical issues because it made it too easy for the protagonist to get back to her own time. To see what I changed the “rings” to, you’ll have to keep up with the story on WattPad!