In the novel "The Emperor" by R.D. Villam there is a scene where 6 people are traveling somewhere riding horses but each of them also brings 2 extra horses, with a horse running at either side of each person.

The scene explained that every 6 hours, they will change their horse so that the horses didn't get too tired. Thus, they can move continuously.

The scene also explained that they only stop 3 times for 2 hours each. Every stop is for resting and letting their horses eat grass.

Is all of this realistic??

\*edit: 
In that scene, the rider arrived at their destination in 2 days.