I'd say cause some time has passed.....
I was told 20 minutes after running but I guess it's in the 10 - 20 minute ballpark. I assume it is to prevent a false reading...so the system lets the warm oil settle before it will display the result.....since you can't wipe the non-existant dip-stick and get a fresh level reading.
Beware of scaring yourself as a few on this site have (including me) by reading when the oil is cold......you'll get an overfill warning!
Cheers,
Kev.

