I’m afraid that is no longer an option, @PeterAD . Fitbit’s explanation is below. You can read more about it here.
To improve your experience with notifications, syncing, and firmware updates, we removed the option to turn off all-day sync from the Fitbit app. When your phone is near your Fitbit device with Bluetooth turned on, it periodically syncs with the Fitbit app to update your stats and download available firmware updates. More frequent syncing rarely, if ever, noticeably decreases your device’s battery life.
