Scheduled Departure will bring the passenger cabin to your preset cabin temperature. You should leave the Climate Control set to Auto and your preferred temperature. Set the fan speed control to Medium or High (In the Climate Control Auto setting the fan speed control is a speed limiter for the maximum fan speed while warming or cooling the passenger cabin.
Scheduled Departure does not affect when charging starts or ends. The Tesla Model Y will draw power if plugged in while preconditioning is active to replenish any charge used while preconditioning. The Tesla Model Y does not have to be plugged in to use Scheduled Departure as long as the battery state of charge is above 20%.
Charging is handled separately:
You can charge as soon as you plug in, or
Set Scheduled Charging, i.e. always start charging at midnight until complete, or
Set Off-peak charging, will determine when to start charging sometime in the early A.M. so that charging will be completed by the end of the off-peak window for lowest electric kWh rate.
Note: You cannot have both Scheduled Charging and Off-peak Charging active at the same time; you must choose whether you want to charge soonest (following a schedule) or complete charging as late as possible while still completing charging by the end of the Off-Peak rate window.
Competing charging as late as possible is more efficient, in winter, as the battery will already be partially warmed from the just completed charging session. Preconditioning the passenger cabin will take less energy if you start preconditioning using coolant from the battery loop that has already been somewhat warmed from the charging session.