There's no single magic number, but there are good principles.
Why short sessions
Young children's attention is limited, and speech is a motor skill that benefits from spaced repetition. Research on learning generally favors practice spread over time rather than crammed into one sitting.
Signs a session is too long
Your child starts guessing or rushing
Tries get sloppier, not better
They resist starting the next day
Count repetitions, not minutes
Ten words with one or two tries each gives a focused set of practice attempts in a few minutes. That's the shape of a SoundSprout mission.
If your SLP gives a number
Use it. Clinicians may recommend specific amounts of practice for your child's goals.
SoundSprout is guided daily practice for one speech sound: ten words, about five minutes, with a warm voice modeling every word. Up to five children per account.
SoundSprout