To, #asNanoSeconds converts the time into the umber of nanosecond that the time represents.
#nanoSeconds (and the others) create a duration that is to be added to the time or DateAndTime. The two do not end with the same things 0 and shouldin't.
The first tells you how many they represent; the second builds duration.
Probably not ideal names - but the intents are definitely different.
-cbc