You may hear nothing at all. Don’t even expect the driver to necessarily say anything. Sometimes they just dump it somewhere near your house and walk off without even letting you know it’s been delivered. It’s totally self service and you will just unlock with the app once your booking starts.
I’d say to expect a text from Gefco on the day. They sometimes give you a code to track it, but if not your app will simply spring to life 30 minutes before the booking start time.
Is there anything specific that your are concerned about and would like to confirm? Maybe we can advise here or you can speak directly to ONTO by phone or live chat too.