Without using a 3rd party service, there isn’t a scheduling function for the climate control.
Is the car close enough to your house/apartment/... to have the phone key connected over the direct Bluetooth connection? If so, the next time you want to warm the car, unlock the doors (and then relock them if you’re not parked in a private locked garage) via the app. If you’re close enough, this can work even if the Internet connection for other functions is down. In almost all cases, you should then be able to turn on the climate control in 5-10 seconds. Unlocking the doors seems to be the nudge needed to wake it from whatever deep sleep state it is in.