Click to download, or see the online graph
Saving to a server means that all your button presses will be sent to the server you specify. Whoever runs that server will be notified when you wake up or go to sleep, so be very careful if someone you don't know asks you to use this feature.
Guidance is useful for people with an average day length different to 24 hours. Say you need to wake up at 9am on December 25th, but you're currently on target to wake up at 3pm that day. Should you go to bed early until Christmas, or push forward instead? Guidance suggests an early and late bed time tonight, plus the number of sleeps and average day lengths you would need to aim for.