Location is only automatic when you have a cell signal. When you upload it manually via satellite, it will show them how many minutes ago you las sent it (since it only lets you do it every 15 minutes).

I tested it a Zion NP last weekend. The service is free for two years, which includes uploading your location via satellite. It only allows you to do it every 15 minutes. When you see the satellite symbol (which appears when you have no cellular signal), go to the Find My app and select “send my location via satellite.” Anyone who shares location with you will then be able to see where you are along with a note that the location was updated via satellite since you have no cellular signal. It took ~28 seconds each time to connect to the satellite and send the location. It guides you to (slightly) move the phone to stay locked onto the satellite as it’s sending.