Apparently someone trying to promote the tale decided to use Harold Hill's name to try to add credibility to the story:
"... Interestingly, some accounts have Mr. Hill as being the man who had attended Sunday school as a small child, and who therefore was responsible for helping the NASA computers find the “missing day” of Joshua. In other accounts, Mr. Hill is simply a man who was present as these events unfolded, and as such is the storyteller. To add to the confusion, some stories leave out Mr. Hill's name, and his part in these events, altogether.
Many have tried, and failed, to document this story. After an article on this subject appeared in the
Bible-Science Newsletter in April 1970, a number of readers of that publication sent letters to Mr. Harold Hill, care of the Curtis Engine Company in Baltimore, Maryland. Their letters, however, were returned with a notation from the Post Office that no such firm existed in Baltimore. In the July 1989 issue of the
Bible-Science Newsletter, there appeared an article which mentions that after the April 1970 publication of the story, some readers finally did receive a form letter from Mr. Hill, in which he stated that he did not write the original article..."
http://creation.com/has-nasa-discovered-a-missing-day