Question About First Day Covers

Hello all. Could use some info on this cover from Fremont Ohio, September 7, 1940, which is the first day Scott #898 was issued. However, I have been unable to find any first day covers for this stamp that do not originate from Albuquerque New Mexico. Wondering why? Also the time is rather odd - 4am. My questions:

When they issued first day covers for this stamp, were they limited to Albuquerque New Mexico? If anyone knows.

What is the best resource (book, etc.) to find out information on how stamps were rolled out?

Is 4am the most likely earliest use of this stamp?

Often, "first day cover" refers to an officially serviced cover with a special handstamp for the day on which the stamp is issued; i.e. a philatelic cover. If stamps can only be cancelled on the day of issue at the facility from which the first day covers originates, you could argue they are not really first day covers.

If the stamp is released throughout the country, people can use them on "normal" mail and the post office cancels the stamp with an "ordinary" cancel. In a way, such covers with a stamp that was cancelled on the day of issue is a much more genuine first day cover. Often it is referred to as "first day of use" or "first day of issue" cover.

Specifically to your cover, hac5x3. The stamp was to be sold only at Albuquerque on September 7th. However, distribution had been made to post offices across the United States with instructions not to sell them before September 8th (or possibly the 9th, since he 7th was a Saturday). Since it would be impossible for someone to obtain the stamp in Albuquerque on September 7th and transport it to Fremont, Ohio in time for a 4 AM postmark, I think it is safe to assume that some postmaster failed to head the do no sell before warning and sold them prematurely.