Learning one subject in an uninterrupted block is suboptimal. Better to divide the subjects and spend a bit of time on each one.
Details
For example, instead of spending 3hrs studying skill A, spend 1hr each on Skill A, B and C.
The harder the practise, teh more effective the learning. Thus interleaving makes it harder.
Forces you to recall actively.
Builds and reinforces connections between concepts or ideas.
References
The Science of Rapid Skill Acquisition: Advanced Methods to Learn, Remember, and Master New Skills, Information, and Abilities - Peter Hollins
Quotes
"[Interleaved learning] advantage over block learning is surprising: interleaving produces a 43% increase in learning and retention over block learning."