There is a structure, but no deadline.
The challenges are organised into 28 days, and each day unlocks in order. The intended pace is one day per day — about 15 minutes — because spacing the material out is genuinely how it sticks.
But nothing expires and nothing locks you out. If you miss a day, your streak resets and the lesson is still there waiting. If you want to do four days in one sitting, you can.
The streak exists to give you a reason to come back tomorrow, not to punish you for a busy week.