Design for twenty minutes, not two hours
The critical property of a fragment-friendly system is zero setup cost. If it takes fifteen minutes to get into a task, a twenty-minute break is useless. What you need is work that can be started in ten seconds and stopped without loss.
- Review due cards. Perfect fragment work: the scheduler already decided what's due, so there is no setup and no decision. Eight cards on a bus is a real review session.
- Practice questions, one at a time. Self-contained, immediate feedback, stoppable anywhere.
- Listen to a recorded lecture on a commute — with timestamped notes to return to so it isn't passive.
- Blurt a topic onto a phone note. Five minutes, no materials needed, and it's genuine retrieval.
What genuinely needs a long block
Some things do: essays, problem sets, anything requiring you to hold a complex structure in your head. Be honest about which, and protect one or two long blocks a week for exactly those — then stop feeling guilty about doing everything else in fragments.
The advantage you actually have
Fragmented study is *forcibly spaced*. You cannot cram, because you don't have the hours to cram with — so you are doing distributed practice by necessity, which is the thing full-time students have to be talked into and mostly aren't.
This is genuinely an advantage, and it's worth knowing, because the guilt of not having long evenings obscures the fact that the long evenings are frequently wasted anyway.