Thanks. That is different than how Tesla does it. Tesla first downloads the image to the vehicle and once it is complete, you are notified that the download is ready and when you choose to start the update, the update will start within 2 min and actual FW update process will begin. The only time I've seen an update available but not ready to install was when the vehicle wasn't on wi-fi and the car would instruct me to connect to wi-fi to download the new FW.
Tesla (like many other consumer electronics) also batches updates and they are not sent to the field all at once. This helps insure that if an issue is found, the update deployment can be stopped before it affects too many vehicles. My last company did this as well for their products. First send out a small batch of updates, wait to see if end users call in with issues, then roll out more day by day.