I started blocking my schedule in 90-minute chunks instead of by task and my productivity actually went up

I used to plan my day around finishing specific things: finish the reading, write the intro, respond to emails. The problem was that tasks always took longer than expected and by noon my whole plan had fallen apart. I switched to blocking 90-minute windows and just working on one subject or project for that entire window regardless of whether I finish the task. When the 90 minutes ends I stop, take a real break, and switch to something else. I'm getting more done because I stopped trying to predict how long things take and started just protecting the time instead. It also made it easier to fit work shifts around studying because the blocks are easier to move than open-ended tasks.