SE is working on a way to jump to certain phases of a raid for practice:
"On a basic level, this raid finder would have the same function as the Duty Finder, but it would primarily address Savage raids with specific participation requirements.

For example, you would be able to select whether you wanted to go for practice or to clear it by checking a box. If you were going into a raid to practice, you would be able to select the beginning, middle, or end phase of the fight."

Source letter from the Producer April 12