Ultradian Cycles
Andrew explains the importance of ultradian cycles, which are 90-minute cycles that our brain and body operate within. He suggests setting a timer for 90 minutes and dropping into focused mental or physical work during that time, accepting occasional flickers of focus and going back to focusing.In this clip
From this podcast

Huberman Lab
Focus Toolkit: Tools to Improve Your Focus & Concentration | Huberman Lab Podcast #88
Related Questions
How should I interpret Andrew Huberman's suggestion that the ideal duration for focused work is 90 minutes but then suggests taking a break every 45 minutes in the episode Maximizing Productivity, Physical & Mental Health with Daily Tools | Huberman Lab Podcast #28 and the clip Ultradian Focus Cycles?
Are the 90-120 minute ultradian cycles all focus time, or is it 70-100 minutes of focus time and 20-minute breaks?
How should I interpret Andrew Huberman's suggestion that the ideal duration for focused work is 90 minutes but also recommends taking a break every 45 minutes in the episode Maximizing Productivity, Physical & Mental Health with Daily Tools | Huberman Lab Podcast #28 and the clip Ultradian Focus Cycles?