To change how long you fast:
Go to your Daily Log
Tap the pencil icon on the Fasting card
Choose a preset duration:
12 hours (12-hour eating window)
14 hours (10-hour eating window)
16 hours (8-hour eating window)
18 hours (6-hour eating window)
Or select Custom and pick any duration from 1-72 hours
Tap Save
Your selection becomes the default for future fasts. The button will update to show your new duration (e.g., "Start 18h fast now").