I certainly wouldn't know when, but I can surely imagine "presently" first being thought of as "Now, instantly", then "REALLY quick now," and then "I have it in mind for current execution, and I'll get it done in just a little bit," and pretty soon forgetting the urgency and expanding the now-built-in delay. A sort of gradual widening of the time parameter, forgetting the initial immediacy.

Dave Oesterreich