You rarely have to start a sync yourself. It runs when your photos change, when you save something, when you press a button, and on a schedule you choose, never two at a time.
The app watches the phone's photo library, even when it is closed. A minute after a photo is added, changed or deleted in a folder you sync (at most five minutes when changes keep coming), a sync runs on its own. It needs a network connection, and runs at most once every 15 minutes for photo changes.
If your folders changed since the last sync, a sync starts.
Tags, people, wording, a place, a named face, an edited photo: the change is finished on the phone, and a sync starts right after to carry it up.
The photos reload and a sync starts.
Re-Sync, Re-read, Documents or Reset on the Sync screen, Re-sync N on a selection, or Save and sync after changing folders.
Right after the phone's index was created or found.
Every day, every week or every month (30 days), your choice, as a safety net: it catches what the phone cannot notice, such as photos waiting to be read after the AI allowance resets. It waits for a network connection and a battery that is not low.
Only one sync ever runs. No button is refused as busy: a button that touches the index stops the running sync first, does its work, then starts the sync again. Stop halts every sync and face reading and holds them: nothing runs again, on its own or on schedule, until you press a button. Everything already indexed stays indexed.
On the Sync screen, under Automatic Re-Sync, choose Every day, Every week or Every month. The new schedule replaces the old one at once; the first automatic run comes one period later.