What happens if, for one reason or another, I need to drive the car when an OTA update is in progress?
Wait 40 minutes. So wait to do at night when you don’t expect to use
You can’t drive the car while an update is being installed. Most updates complete in less than 20 minutes (regardless of the estimated time shown). Plan accordingly.
The time depends on the car. For the HW 1.0 (pre 2017 S/X) cars, the update time takes longer than the Model 3 update takes.
The update shows you approximately how long it will take to apply. Do not start the update if there is any chance you might need the car. I typically do it either at night while I am home, or as I pull into work.
I usually just install at night at home. I don’t want to be stranded somewhere if by chance the update causes an issue with the car. (Not that I’ve heard of that happening.)
I would judge it like your phone. Do not install any software updates in a period of time when you think you'll need the vehicle or device to be used. Agree with everyone on the notion of doing it at home at night so that if there are any problems you dont have to worry about not getting back home that day. I'd rather be stranded at home than be stranded at work.
@mcdonalk: Have you seen an update come through yet? If not, it works like this: the car and the phone app notify you that an update is available, then gives you the option to schedule it, or dismiss it for a while. As others have said, schedule it for a time when you’re asleep and don’t worry about it!
You also can't drive an ICE vehicle while it is being serviced.