Where to hang the cue

The best cue is something that already happens without you arranging it.

The prayers are the obvious candidate. Five fixed points, distributed across the day, already installed, and each one is a natural boundary. After Fajr. After Maghrib. Nobody is adding an obligation here and nothing about your prayer changes. The timetable simply already exists, and you can hang a study start on it.

Other cues that work the same way: when I get off the bus, when I have put my bag down, when I have washed up after dinner. What does not work is a cue like when I feel ready, because that is not a moment. That is the decision you were trying to remove.